Semiconductor device, and manufacturing method of semiconductor device

ABSTRACT

In order to form a plurality of semiconductor elements over an insulating surface, in one continuous semiconductor layer, an element region serving as a semiconductor element and an element isolation region having a function to electrically isolate element regions from each other by repetition of PN junctions. The element isolation region is formed by selective addition of an impurity element of at least one or more kinds of oxygen, nitrogen, and carbon and an impurity element that imparts an opposite conductivity type to that of the adjacent element region in order to electrically isolate elements from each other in one continuous semiconductor layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device having aplurality of semiconductor elements and a manufacturing method thereof.

2. Description of the Related Art

In a case where a plurality of semiconductor elements are provided overan insulating surface, a method is employed, by which a semiconductorfilm formed over an insulating surface is processed by etchingprocessing into a plurality of island-shaped semiconductor layers. Thesemiconductor element has a stacked structure of a plurality of thinfilms, and in a case of a planar type thin film transistor, a gateinsulating layer is stacked to cover semiconductor layers divided intoisland shapes.

The semiconductor layers processed into island shapes have steps in edgeportions thereof, and accordingly, defects such as thinning of the gateinsulating layer and breakage of a film are generated.

When the gate insulating layer is thinned, a characteristic defect of asemiconductor device is generated, such as leakage current flowingbetween a gate electrode and the semiconductor layer and a short-circuit(a short) caused by contact between the gate electrode and thesemiconductor layer.

In order to solve the above-described problems, a method is conducted,in which two gate insulating layers having different shapes are stackedto relieve steps resulting from the edge portion of the semiconductorlayer and to improve coverage (for example, see Patent Document 1:Japanese Published Patent Application No. H10-242471).

SUMMARY OF THE INVENTION

However, by such a method of relieving steps, defects such as a shortcaused by contact between a semiconductor layer and a gate electrode andleakage current cannot be prevented sufficiently depending on athickness of a semiconductor layer and a gate insulating layer. Inparticular, there has been a problem that the leakage currentsignificantly occurs in a case where a semiconductor element isminiaturized (for example, a gate length is less than or equal to 1 μm).

It is an object of the present invention to provide a highly reliablesemiconductor device in which defects such as a short and leakagecurrent between a gate electrode and a semiconductor layer that arecaused by a coverage defect of a semiconductor layer with a gateinsulating layer are prevented, and a manufacturing method of such asemiconductor device.

In the present invention, in order to form a plurality of semiconductorelements over an insulating surface, without dividing a semiconductorlayer into a plurality of island-shaped semiconductor layers, an elementregion serving as a semiconductor element and an element isolationregion having a function of electrically insulating and isolatingelement regions that has high resistance and forms a PN junction withthe element region are formed in one continuous semiconductor layer.

The element isolation region is formed by selective addition of a firstimpurity element that does not contribute to improvement in conductivityand a second impurity element that imparts an opposite conductivity typeto that of the source region and the drain region in the element regionin order to electrically isolate elements from each other in onecontinuous semiconductor layer. It is to be noted that the expression“an object that does not contribute to conductivity” is used for themeaning “an object that does not contribute to improvement inconductivity”.

As the first impurity element that does not contribute to conductivity,an impurity element of at least one or more kinds of oxygen, nitrogen,and carbon can be used. In the element isolation region to which thefirst impurity element is added, conductivity is lowered by mixture ofthe first impurity element that does not contribute to conductivity, andresistance of the element isolation region is increased because itscrystallinity is lowered by a physical impact (it can also be referredto as a so-called sputtering effect) on the semiconductor layer atadding. In the element isolation region with the increased resistance,electron field-effect mobility is also lowered, and accordingly,elements can be electrically isolated from each other. On the otherhand, in a region to which an impurity element is not added, electronfield-effect mobility that is high enough to be able to serve as anelement is kept, and accordingly, the region can be used as an elementregion.

The element region has a source region, a drain region, and a channelformation region. The source region and the drain region are impurityregions having one conductivity type (for example, n-type impurityregions or p-type impurity regions). An impurity element that imparts anopposite conductivity type to that of the source region and the drainregion in the element region is added to the element isolation region,whereby the element isolation region is made to be an impurity regionhaving an opposite conductivity type to that of the source region andthe drain region in the adjacent element region. That is, in a casewhere the source region and the drain region in the element region aren-type impurity regions, the adjacent element isolation region may beformed as a p-type impurity region. Similarly, in a case where thesource region and the drain region in the element region are p-typeimpurity regions, the adjacent element isolation region may be formed asan n-type impurity region. The element region and the element isolationregion that are adjacent to each other form a PN junction. Accordingly,the element regions can be further insulated and isolated from eachother by the element isolation region provided between the elementregions.

One, feature of the present invention is that one continuoussemiconductor layer is isolated into a plurality of element regions inthe manner that resistance of the element isolation region by which theelement regions are insulated and isolated from each other is increasedby addition of the first impurity element that does not contribute toconductivity, and further, a PN junction is formed in a position wherethe element region and the element isolation region are in contact witheach other by addition of the second impurity element that imparts anopposite conductivity type to that of the source region and the drainregion in the element region. By the present invention, the elementregions can be isolated from each other by an effect caused by each ofthe first impurity element and the second impurity element. Thus, ahigher effect of insulation and isolation of the element can beobtained.

It is to be noted that, in this specification, an element regionincludes an element formation region in which an element has not beenformed yet. Therefore, even when an element is not completed in themanufacturing step of the element (at the stage before other electrodelayers or insulating layers are formed), an element formation regionthat is insulated and isolated from another element formation region byan element isolation region that is a high-resistance region provided inthe semiconductor layer will be called an element region.

The addition (introduction) of the impurity element that does notcontribute to conductivity in forming the element isolation region canbe performed by an ion implantation method, an (ion) doping method, orthe like.

Further, in the element isolation region, the first impurity element andthe second impurity element may have concentration gradients. Forexample, in a case where the element isolation region is formed in thesemiconductor layer provided over the substrate, in the elementisolation region, the second impurity element may be selectively addedat higher concentration on the substrate side, and the first impurityelement may be selectively added at higher concentration on thesemiconductor layer surface side. Of course, the first impurity elementand the second impurity element may be added at approximately uniformconcentration in the element isolation region. That is, the peakconcentration of the first impurity element and the peak concentrationof the second impurity element can be appropriately set in the elementisolation region.

The resistivity of the element isolation region is preferably greaterthan or equal to 1×10¹⁰ Ω·cm, and the concentration of the firstimpurity element such as oxygen, nitrogen, or carbon is preferablygreater than or equal to 1×10²⁰ Ω·cm⁻³ and less than 4×10²² Ω·cm⁻³.

Crystallinity of the element isolation region is lowered by addition ofthe impurity element; therefore, it can be said that the elementisolation region is made to be amorphous. On the other hand, because theelement region is a crystalline semiconductor layer, in a case where asemiconductor element is formed in the element region, crystallinity ofthe channel formation region is higher than that of the elementisolation region, and high electron field-effect mobility can beobtained as a semiconductor element.

As the impurity element added to the element isolation region, a raregas element such as argon (Ar), neon (Ne), krypton (Kr), or xenon (Xe)may be used. By further addition of such a rare gas element that is anelement having comparatively high mass as well as oxygen, nitrogen, andcarbon, a physical impact on the semiconductor layer can be increased,whereby crystallinity of the element isolation region can be loweredmore effectively.

Therefore, with the use of the present invention, a semiconductor layercan be isolated into a plurality of element regions without beingdivided into island shapes. Steps resulting from the edge portion of thesemiconductor layer are not generated. Thus, a gate insulating layer isformed over a flat semiconductor layer, leading to improvement incoverage of the semiconductor layer with the gate insulating layer.Accordingly, the present invention can provide a highly reliablesemiconductor device in which defects such as a short and leakagecurrent between the gate electrode and the semiconductor layer that arecaused by a coverage defect of the semiconductor layer with the gateinsulating layer are prevented, and a manufacturing method of such asemiconductor device.

It is to be noted that in the present invention, a semiconductor devicerefers to a device which can function by utilizing the semiconductorcharacteristics. With the use of the present invention, a device havinga circuit including semiconductor elements (e.g., transistors, memoryelements, and/or diodes) or a semiconductor device such as a chipincluding a processor circuit can be manufactured.

One mode of a semiconductor device of the present invention includes,over an insulating surface, a semiconductor layer including an elementisolation region and an element region, where the element regionincludes a source region, a drain region, and a channel formationregion; the element isolation region and the element region are incontact with each other; the element isolation region includes a firstimpurity element and a second impurity element; the first impurityelement is at least one or more kinds of oxygen, nitrogen, and carbon;the second impurity element is an impurity element that imparts anopposite conductivity type to that of the source region and the drainregion to the element isolation region; and crystallinity of the elementisolation region is lower than that of the channel formation region.

Another mode of a semiconductor device of the present inventionincludes, over an insulating surface, a semiconductor layer including anelement isolation region, and a first element region and a secondelement region that are adjacent to each other with the elementisolation region interposed therebetween, where the first element regionincludes a first source region, a first drain region, and a firstchannel formation region; the second element region includes a secondsource region, a second drain region, and a second channel formationregion; the first source region, the first drain region, the secondsource region, and the second drain region have the same conductivitytype; the element isolation region includes a first impurity element anda second impurity element; the first impurity element is at least one ormore kinds of oxygen, nitrogen, and carbon; the second impurity elementis an impurity element that imparts an opposite conductivity type tothat of the first source region, the first drain region, the secondsource region, and the second drain region to the element isolationregion; and crystallinity of the element isolation region is lower thanthat of the first channel formation region and the second channelformation region.

Another mode of a semiconductor device of the present inventionincludes, over an insulating surface, a semiconductor layer including afirst element region, a first element isolation region, a second elementisolation region, and a second element region, where the first elementregion includes a first source region, a first drain region, and a firstchannel formation region; the second element region includes a secondsource region, a second drain region, and a second channel formationregion; the first source region and the first drain region are n-typeimpurity regions; the second source region and the second drain regionare p-type impurity regions; the first element isolation region includesa first impurity element of at least one or more kinds of oxygen,nitrogen, and carbon and an impurity element that imparts p-typeconductivity to the first element isolation region; the second elementisolation region includes a first impurity element of at least one ormore kinds of oxygen, nitrogen, and carbon and an impurity element thatimparts n-type conductivity to the second element isolation region; andcrystallinity of the first element isolation region and the secondelement isolation region is lower than that of the first channelformation region and the second channel formation region.

Another mode of a manufacturing method of a semiconductor device of thepresent invention includes the steps of forming a semiconductor layerover an insulating surface, forming an element region and an elementisolation region that includes a first impurity element and a secondimpurity element in the semiconductor layer by selective addition of thefirst impurity element of at least one or more kinds of oxygen,nitrogen, and carbon and the second impurity element that imparts oneconductivity type, to the semiconductor layer, forming an insulatinglayer over the element region and the element isolation region, forminga conductive layer over the element region and the insulating layer, andforming a source region and a drain region having an oppositeconductivity type to that of the channel formation region and the secondimpurity element in the element region.

Another mode of a manufacturing method of a semiconductor device of thepresent invention includes the steps of forming a semiconductor layerover an insulating surface, forming an element region and an elementisolation region including a first impurity element and a secondimpurity element in the semiconductor layer by selective addition of thefirst impurity element of at least one or more kinds of oxygen,nitrogen, and carbon and the second impurity element that imparts oneconductivity type, to the semiconductor layer, forming an insulatinglayer over the element region and the element isolation region, forminga conductive layer over the element region and the insulating layer, andforming a source region and a drain region having an oppositeconductivity type to that of the channel formation region and theelement isolation region in the element region by addition of animpurity element that imparts an opposite conductivity type to that ofthe second impurity element to the element region.

Another mode of a manufacturing method of a semiconductor device of thepresent invention includes the steps of forming a semiconductor layerover an insulating surface, forming an insulating layer over thesemiconductor layer, forming an element region and an element isolationregion including a first impurity element and a second impurity elementin the semiconductor layer by selective addition of the first impurityelement of at least one or more kinds of oxygen, nitrogen, and carbonand the second impurity element that imparts one conductivity type, tothe semiconductor layer through the insulating layer, forming aconductive layer over the element region and the insulating layer, andforming a source region and a drain region having an oppositeconductivity type to that of a channel formation region and the secondimpurity element in the element region.

Another mode of a manufacturing method of a semiconductor device of thepresent invention includes the steps of forming a semiconductor layerover an insulating surface, forming an insulating layer over thesemiconductor layer, forming an element region and an element isolationregion including a first impurity element and a second impurity elementin the semiconductor layer by selective addition of the first impurityelement of at least one or more kinds of oxygen, nitrogen, and carbonand the second impurity element that imparts one conductivity type, tothe semiconductor layer through the insulating layer, forming aconductive layer over the element region and the insulating layer, andforming a source region and a drain region having an oppositeconductivity type to that of a channel formation region and the elementisolation region in the element region by selective addition of animpurity element that imparts an opposite conductivity type to thesecond impurity element, to the element region.

Therefore, with the use of the present invention, a semiconductor layercan be isolated into a plurality of element regions without beingdivided into island shapes. Hence, steps resulting from the edge portionof the semiconductor layer are not generated, and thus a gate insulatinglayer is formed over a flat semiconductor layer, leading to improvementin coverage of the semiconductor layer with the gate insulating layer.

Accordingly, a highly reliable semiconductor device in which defectssuch as a short and leakage current between a gate electrode and asemiconductor layer that are caused by a coverage defect of asemiconductor layer with a gate insulating layer are prevented, and amanufacturing method of such a semiconductor device can be provided.Hence, miniaturization and high integration can be further performed ina semiconductor device, and high performance of the semiconductor devicecan be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C are views illustrating a top view and cross-sectionalviews of a semiconductor device of the present invention;

FIGS. 2A to 2C are views illustrating a top view and cross-sectionalviews of a semiconductor device of the present invention;

FIGS. 3A to 3D are views illustrating cross sectional views of asemiconductor device of the present invention;

FIGS. 4A to 4C are views illustrating a top view and cross-sectionalviews of a semiconductor device of the present invention;

FIGS. 5A to 5F are views illustrating a manufacturing method of asemiconductor device of the present invention;

FIGS. 6A to 6E are views illustrating a manufacturing method of asemiconductor device of the present invention;

FIGS. 7A to 7F are views illustrating a manufacturing method of asemiconductor device of the present invention;

FIGS. 8A to 8E are views illustrating a manufacturing method of asemiconductor device of the present invention;

FIGS. 9A to 9C are views illustrating a manufacturing method of asemiconductor device of the present invention;

FIGS. 10A to 10C are views illustrating a manufacturing method of asemiconductor device of the present invention;

FIGS. 11A and 11B are views respectively illustrating a top view and across-sectional view of a semiconductor device of the present invention;

FIG. 12 is a diagram showing an example of an equivalent circuit of asemiconductor device;

FIG. 13 is a diagram showing an example of an equivalent circuit of asemiconductor device;

FIG. 14 is a diagram showing an example of an equivalent circuit of asemiconductor device;

FIG. 15 is a view illustrating a top view of a semiconductor device ofthe present invention;

FIGS. 16A and 16B are views illustrating cross-sectional views of asemiconductor device of the present invention;

FIG. 17 is a view illustrating a top view of a semiconductor device ofthe present invention;

FIGS. 18A and 18B are views illustrating cross-sectional views of asemiconductor device of the present invention;

FIG. 19 is a diagram showing an example of a circuit block diagram of asemiconductor device;

FIGS. 20A to 20D are views illustrating top views of a semiconductordevice of the present invention;

FIGS. 21A to 21G are views illustrating application examples of asemiconductor device of the present invention;

FIGS. 22A to 22C are views illustrating application examples of asemiconductor device of the present invention;

FIGS. 23A to 23E are views illustrating application examples of asemiconductor device of the present invention;

FIGS. 24A and 24B are diagrams illustrating a writing operation of asemiconductor device;

FIGS. 25A and 25B are diagrams illustrating an erasing operation and areading operation of a semiconductor device;

FIGS. 26A to 26C are views illustrating a top view and cross-sectionalviews of a semiconductor device of the present invention;

FIGS. 27A to 27C are views illustrating a top view and cross-sectionalviews of a semiconductor device of the present invention; and

FIGS. 28A to 28D are views illustrating cross-sectional views of asemiconductor device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment Modes of the present invention will be described below indetail with reference to the drawings. However, the present invention isnot limited to explanation to be given below, and it is to be easilyunderstood that various changes in modes and details thereof will beapparent to those skilled in the art without departing from the purposeand the scope of the present invention. Therefore, the present inventionshould not be interpreted as being limited to the description of theembodiment modes to be given below. It is to be noted that, inembodiment of the present invention to be described below, the sameportions or portions having a similar function are denoted by the samereference numerals through different drawings, and repetitiveexplanation thereof will be omitted.

Embodiment Mode 1

In this embodiment mode, as an example of a highly reliablesemiconductor device in which defects such as a short and leakagecurrent between a gate electrode layer and a semiconductor layer thatare caused by a coverage defect of a semiconductor layer with a gateinsulating layer are prevented, an NMOS (N-channel Metal OxideSemiconductor) and a CMOS (Complementary Metal Oxide Semiconductor) willbe described with reference to drawings.

FIGS. 1A to 1C show an example of a semiconductor device with an NMOSstructure of this embodiment mode. FIG. 1A is a top view, FIG. 1B is across-sectional view taken along a line Q-R in FIG. 1A, and FIG. 1C is across-sectional view taken along a line S-T in FIG. 1A.

Over a substrate 600 over which an insulating layer 601 serving as abase film of a semiconductor layer is formed, an NMOS structure having atransistor 610 a that is an n-channel thin film transistor and atransistor 610 b that is an n-channel transistor, and an insulatinglayer 606 are formed. The transistor 610 a includes an element regionhaving n-type impurity regions 607 a and 607 b and a channel formationregion 609 a, and a gate electrode layer 605 a. The transistor 610 bincludes an element region having n-type impurity regions 608 a and 608b and a channel formation region 609 b, and a gate electrode layer 605b. A gate insulating layer 604 and an insulating layer 606 are formedcontiguous with the transistor 610 a and the transistor 610 b. Further,a wiring layer 611 a that is a source electrode layer or a drainelectrode layer connected to the n-type impurity region 607 a, a wiringlayer 611 b that is a source electrode layer or a drain electrode layerconnected to the n-type impurity region 607 b and the n-type impurityregion 608 a, and a wiring layer 611 c that is a source electrode layeror a drain electrode layer connected to the n-type impurity region 608 bare provided, and the transistor 610 a and the transistor 610 b areelectrically connected to each other by the wiring layer 611 b (seeFIGS. 1A to 1C).

In the semiconductor layer, the element region having the n-typeimpurity regions 607 a and 607 b and the channel formation region 609 aincluded in the transistor 610 a and the element region having then-type impurity regions 608 a and 608 b and the channel formation region609 b included in the transistor 610 b are electrically isolated fromeach other by an element isolation region 602 (602 a, 602 b, 602 c, 602d, and 602 e).

FIGS. 4A to 4C show an example of a semiconductor device with a CMOSstructure of this embodiment mode. FIG. 4A is a top view, FIG. 4B is across-sectional view taken along a line A-B in FIG. 4A, and FIG. 4C is across-sectional view taken along a line C-D in FIG. 4A.

Over a substrate 200 over which an insulating layer 201 serving as abase film of a semiconductor layer is formed, a CMOS structure having atransistor 210 a that is an n-channel thin film transistor and atransistor 210 b that is a p-channel thin film transistor, and aninsulating layer 206 are formed. The transistor 210 a includes anelement region having n-type impurity regions 207 a and 207 b and achannel formation region 209 a, and a gate electrode layer 205 a. Thetransistor 210 b includes an element region having p-type impurityregions 208 a and 208 b and a channel formation region 209 b, and a gateelectrode layer 205 b. A gate insulating layer 204 and the insulatinglayer 206 are formed contiguous with the transistor 210 a and 210 b.Further, a wiring layer 211 a that is a source electrode layer or adrain electrode layer connected to the n-type impurity region 207 a, awiring layer 211 b that is a source electrode layer or a drain electrodelayer connected to the n-type impurity region 207 b and the p-typeimpurity region 208 a, and a wiring layer 211 c that is a sourceelectrode layer or a drain electrode layer connected to the p-typeimpurity region 208 b are provided, and the transistor 210 a and thetransistor 210 b are electrically connected to each other by the wiringlayer 211 b (see FIGS. 4A to 4C).

In the semiconductor layer, the element region having the n-typeimpurity regions 207 a and 207 b and the channel formation region 209 aincluded in the transistor 210 a and the element region having thep-type impurity regions 208 a and 208 b and the channel formation region209 b included in the transistor 210 b are electrically isolated fromeach other by an element isolation region 202 (202 a, 202 b, 202 c, and202 d) and an element isolation region 212 (212 a and 212 b).

The element isolation region is formed by selective addition of a firstimpurity element that does not contribute to conductivity and a secondimpurity element that imparts an opposite conductivity type to that of asource region and a drain region in the element region, in order toelectrically isolate elements from each other in one semiconductorlayer. As the first impurity element that does not contribute toconductivity, an impurity element of at least one or more kinds ofoxygen, nitrogen, and carbon can be used. In the element isolationregion to which the first impurity element is added, conductivity islowered by mixture of the first impurity element that does notcontribute to conductivity, and resistance of the element isolationregion is increased because its crystallinity is lowered by a physicalimpact (it can also be referred to as a so-called sputtering effect) onthe semiconductor layer at adding. In the element isolation region withthe increased resistance, electron field-effect mobility is alsolowered, and accordingly, elements can be electrically isolated fromeach other. On the other hand, in a region to which an impurity elementis not added, electron field-effect mobility that is high enough to beable to serve as an element is kept, and accordingly, the region can beused as an element region.

The element region has a source region, a drain region, and a channelformation region. The source region and the drain region are impurityregions having one conductivity type (for example, n-type impurityregions or p-type impurity regions). An impurity element that imparts anopposite conductivity type to that of the source region and the drainregion in the element region is added to the element isolation region,whereby the element isolation region is made to be an impurity regionhaving an opposite conductivity type to that of the source region andthe drain region in the adjacent element region. That is, in a casewhere the source region and the drain region in the element region aren-type impurity regions, the adjacent element isolation region may beformed as a p-type impurity region. Similarly, in a case where thesource region and the drain region in the element region are p-typeimpurity regions, the adjacent element isolation region may be formed asan n-type impurity region. The element region and the element isolationregion that are adjacent to each other form a PN junction. Accordingly,the element regions can be further insulated and isolated from eachother by the element isolation region provided between the elementregions.

One feature of the present invention is that one semiconductor layer isisolated into a plurality of element regions in the manner thatresistance of the element isolation region by which the element regionsare insulated and isolated from each other is increased by addition ofthe first impurity element that does not contribute to conductivity, andfurther, a PN junction is formed in a position where the element regionand the element isolation region are in contact with each other byaddition of the second impurity element that imparts an oppositeconductivity type to that of the source region and the drain region inthe element region. By the present invention, the element regions can beisolated from each other by an effect caused by each of the firstimpurity element and the second impurity element. Thus, a higher effectof insulation and isolation of the element can be obtained.

FIGS. 1A to 1C show a case where a plurality of n-channel thin filmtransistors are formed. Because the element isolation region 602 (602 a,602 b, 602 c, 602 d, and 602 e) is provided to be in contact with then-type impurity regions 607 a, 607 b, 608 a, and 608 b, the elementisolation region 602 may be formed as a p-type impurity region byaddition of an impurity element that imparts p-type conductivity (forexample, boron (B), aluminum (Al), gallium (Ga), or the like) as asecond impurity element that imparts an opposite conductivity type tothat of the n-type impurity regions 607 a, 607 b, 608 a, and 608 b.

Although an NMOS structure is shown as an example in this embodimentmode, a PMOS structure is also employed in the similar manner. Becausethe source region and the drain region in the element region are p-typeimpurity regions, a second impurity element that imparts n-typeconductivity may be added so that the adjacent element isolation regionbecomes an n-type impurity region. Accordingly, the present inventioncan employ any of an NMOS structure, a PMOS structure, and a CMOSstructure.

FIGS. 4A to 4C show a case where a CMOS structure is formed. Because theelement isolation region 202 (202 a, 202 b, 202 c, and 202 d) isprovided to be in contact with the n-type impurity regions 207 a and 207b, the element isolation region 202 may be formed as a p-type impurityregion by addition of an impurity element that imparts p-typeconductivity (for example, boron (B), aluminum (Al), gallium (Ga), orthe like) as a second impurity element that imparts an oppositeconductivity type to that of the n-type impurity regions 207 a and 207b.

On the other hand, because the element isolation region 212 (212 a and212 b) is provided to be in contact with the p-type impurity regions 208a and 208 b, the element isolation region 212 may be formed as an n-typeimpurity region by addition of an impurity element that imparts n-typeconductivity (for example, phosphorus (P), arsenic (Ar), or the like) asa second impurity element that imparts an opposite conductivity type tothat of the p-type impurity regions 208 a and 208 b. As a result, ann-type impurity region and a p-type impurity region are alternatelyprovided to be adjacent to each other, and accordingly, impurity regionshaving the same conductivity type can be insulated and isolated fromeach other.

The addition (introduction) of the first impurity element and the secondimpurity element in forming the element isolation region can beperformed by an ion implantation method, an (ion) doping method, or thelike.

Further, in the element isolation region, the first impurity element andthe second impurity element may have concentration gradients. Forexample, in a case where the element isolation region is formed in thesemiconductor layer provided over the substrate, in the elementisolation region, the second impurity element may be selectively addedat higher concentration on the substrate side, and the first impurityelement may be selectively added at higher concentration on thesemiconductor layer surface side. Of course, the first impurity elementand the second impurity element may be added at approximately uniformconcentration in the element isolation region. That is, the peakconcentration of the first impurity element and the peak concentrationof the second impurity element can be appropriately set in the elementisolation region.

An example of adding the first impurity element and the second impurityelement in the element isolation region will be described with referenceto FIGS. 3A to 3D and FIGS. 28A to 28D. FIGS. 3A to 3D show a case wheresource regions and drain regions included in element regions isolated byelement isolation regions have the same conductivity, like an NMOSstructure or a PMOS structure. FIGS. 28A to 28D show a case where sourceregions and drain regions included in element regions isolated byelement isolation regions have an opposite conductivity type to eachother, like a CMOS structure.

In FIGS. 3A to 3D, over a substrate 700 provided with an insulatinglayer 701, a semiconductor layer 702 including element isolation regions703 a, 703 b, and 703 c, n-type impurity regions 704 a and 704 b, andn-type impurity regions 705 a and 705 b is formed, and over thesemiconductor layer 702, conductive layers 708 a and 708 b are formedwith an insulating layer 709 interposed between the semiconductor layer702 and the conductive layers 708 a and 708 b.

The element isolation region is formed by addition of the first impurityelement and the second impurity element as described above. The elementisolation regions 703 a, 703 b, and 703 c in FIG. 3A show an example inwhich a first impurity element that is an impurity element of at leastone or more kinds of oxygen, nitrogen, and carbon and the secondimpurity element that imparts an opposite conductivity type to that ofthe source region and the drain region in the element region areincluded almost uniformly. An impurity element that imparts p-typeconductivity is used as the second impurity element because the sourceregion and the drain region in the element region are n-type impurityregions. Accordingly, the element isolation regions 703 a, 703 b, and703 c become p-type impurity regions. The element isolation regions 703a, 703 b, and 703 c are provided between the n-type impurity regions 704a and 704 b and the n-type impurity regions 705 a and 705 b, leading toPN junctions. Hence, an element region having the n-type impurityregions 704 a and 704 b and a channel formation region 706 a and anelement region having the n-type impurity regions 705 a and 705 b and achannel formation region 706 b can be insulated and isolated from eachother .

An element isolation region in FIG. 3B has a stacked structure of firstelement isolation regions 713 a, 713 b, and 713 c and second elementisolation regions 714 a, 714 b, and 714 c, respectively. However, thefirst element isolation region and the second element isolation regionare not formed using a stack of thin films but are regions to which afirst impurity element and a second impurity element are added;therefore, their boundaries are not clear. The first element isolationregions 713 a, 713 b, and 713 c are regions to which the second impurityelement that imparts an opposite conductivity type to that of the sourceregion and the drain region in the element region is added, and thesecond element isolation regions 714 a, 714 b, and 714 c are regions towhich the first impurity element that does not contribute toconductivity is added. In such a manner, in the element isolationregion, the first impurity element and the second impurity element maybe selectively added, and each of the first impurity element and thesecond impurity element may have concentration gradients in the elementisolation region.

An element isolation region in FIG. 3C has a stacked structure of firstelement isolation regions 719 a, 719 b, and 719 c and second elementisolation regions 718 a, 718 b, and 718 c, respectively. The secondelement isolation regions 718 a, 718 b, and 718 c are regions to whichthe second impurity element that imparts an opposite conductivity typeto that of the source region and the drain region in the element regionis added, and the first element isolation regions 719 a, 719 b, and 719c are regions to which the first impurity element that does notcontribute to conductivity is added.

An element isolation region in FIG. 3D has a stacked structure of firstelement isolation regions 724 a, 724 b, and 724 c and second elementisolation regions 723 a, 723 b, and 723 c, respectively. The secondelement isolation regions 723 a, 723 b, and 723 c are regions to whichthe second impurity element that imparts an opposite conductivity typeto that of the source region and the drain region in the element regionis added, and the first element isolation regions 724 a, 724 b, and 724c are regions to which the first impurity element that does notcontribute to conductivity is added. As described above, a structure maybe employed, where the region to which the second impurity element isadded is provided in a center portion of the semiconductor layer in athickness direction.

In FIGS. 28A to 28D, over a substrate 700 provided with an insulatinglayer 701, a semiconductor layer 732 including element isolation regions733 a and 733 b, element isolation regions 739 a and 739 b, n-typeimpurity regions 734 a and 734 b, and p-type impurity regions 735 a and735 b is formed, and over the semiconductor layer 732, conductive layers738 a and 738 b are fowled with an insulating layer 709 interposedbetween the semiconductor layer 732 and the conductive layers 738 a and738 b.

The element isolation region is formed by addition of the first impurityelement and the second impurity element as described above. The elementisolation regions 733 a and 733 b and the element isolation regions 739a and 739 b in FIG. 28A show an example in which a first impurityelement that is an impurity element of at least one or more kinds ofoxygen, nitrogen, and carbon and a second impurity element that impartsan opposite conductivity type to that of the source region and the drainregion in the element region are included almost uniformly. An impurityelement that imparts p-type conductivity is used as the second impurityelement in the element isolation regions 733 a and 733 b because thesource region and the drain region in the adjacent element region aren-type impurity regions 734 a and 734 b. Accordingly, the elementisolation regions 733 a and 733 b become p-type impurity regions. Theelement isolation regions 733 a and 733 b are provided by interposingthe n-type impurity regions 734 a and 734 b, leading to PN junctions. Onthe other hand, an impurity element that imparts n-type conductivity isused as the second impurity element in the element isolation region 739a and 739 b because the source region and the drain region in theadjacent element region are p-type impurity regions 735 a and 735 b.Accordingly, the element isolation regions 739 a and 739 b become n-typeimpurity regions. The element isolation regions 739 a and 739 b areprovided by interposing the p-type impurity regions 735 a and 735 b,leading to PN junctions. Hence, an element region having the n-typeimpurity regions 734 a and 734 b and a channel formation region 736 aand an element region having the p-type impurity regions 735 a and 735 band a channel formation region 736 b can be insulated and isolated fromeach other.

As an element isolation region in FIG. 28B, first element isolationregions 741 a and 741 b interposing n-type impurity regions 734 a and734 b are provided and second element isolation regions 742 a and 742 binterposing p-type impurity regions 735 a and 735 b are provided. Thefirst element isolation regions 741 a and 741 b are formed by additionof an impurity element that imparts p-type conductivity as the secondimpurity element, and the second element isolation regions 742 a and 742b are formed by addition of an impurity element that imparts n-typeconductivity. Further, third element isolation regions 740 a, 740 b, and740 c including the first impurity element are formed over the firstelement isolation regions 741 a and 741 b and the second elementisolation regions 742 a and 742 b. In such a manner, in the elementisolation region, the first impurity element and the second impurityelement may be selectively added, and each of the first impurity elementand the second impurity element may have concentration gradients in theelement isolation region.

An element isolation region in FIG. 28C has a stacked structure of firstelement isolation regions 746 a and 746 b to which an impurity elementthat imparts p-type conductivity is added as the second impurity elementand second element isolation regions 747 a and 747 b to which animpurity element that imparts n-type conductivity is added as the secondimpurity element, respectively, over third element isolation region 745a, 745 b, and 745 c to which the first impurity element is added.

An element isolation region in FIG. 28D has a stacked structure of firstelement isolation regions 751 a and 751 b to which an impurity elementthat imparts p-type conductivity is added as the second impurity elementand second element isolation regions 752 a and 752 b to which animpurity element that imparts n-type conductivity is added as the secondimpurity element, respectively, over third element isolation region 750a, 750 b, and 750 c to which the first impurity element is added. Asdescribed above, a structure may be employed, where a region to which animpurity element is added is provided in a center portion of thesemiconductor layer in a thickness direction.

As described above, in the present invention, the first impurity elementand the second impurity element are included in the element isolationregion. However, the first impurity element and the second impurityelement may be selectively added, and at least one of the first impurityelement and the second impurity element may be added. Of course, one ofthe first impurity element and the second impurity element can be addedto the entire element isolation region and the other can be selectivelyadded.

The resistivity of the element isolation region is preferably greaterthan or equal to 1×10¹⁰ Ω·cm, and the concentration of the firstimpurity element such as oxygen, nitrogen, or carbon is preferablygreater than or equal to 1×10²⁰ Ω·cm⁻³ and less than 4×10²² Ω·cm⁻³.

Crystallinity of the element isolation region is lowered by addition ofthe impurity element; therefore, it can be said that the elementisolation region is made to be amorphous. On the other hand, because theelement region is a crystalline semiconductor layer, in a case where asemiconductor element is formed in the element region, crystallinity ofthe channel formation region is higher than that of the elementisolation region, and high electron field-effect mobility can beobtained as a semiconductor element.

As the impurity element added to the element isolation region, a raregas element such as argon (Ar), neon (Ne), krypton (Kr), or xenon (Xe)may be used. By further addition of such a rare gas element that is anelement having comparatively high mass as well as oxygen, nitrogen, andcarbon, a physical impact on the semiconductor layer can be increased,whereby crystallinity of the element isolation region can be loweredmore effectively.

In FIG. 1C, a gate electrode layer 605 is formed to extend over thechannel formation region 609 a and the element isolation regions 602 dand 602 e in the semiconductor layer, with the gate insulating layer 604interposed between the gate electrode layer 605 and the semiconductorlayer. In the present invention, the element isolation region and theelement region are provided in the continuous semiconductor layer;therefore, the element isolation regions 602 d and 602 e and the elementregion, which is the channel formation region 609 a, are contiguous.Thus, the surface thereof has high flatness and no steep step.

Similarly, in FIG. 4C, a gate electrode layer 205 is formed to extendover the channel formation region 209 a and the element isolationregions 202 d and 202 e in the semiconductor layer, with the gateinsulating layer 204 interposed between the gate electrode layer 205 andthe semiconductor layer. In the present invention, the element isolationregion and the element region are provided in the continuoussemiconductor layer; therefore, the element isolation regions 202 c and202 d and the element region, which is the channel formation region 209a, are contiguous. Thus, the surface thereof has high flatness and nosteep step.

Each of the gate insulating layers 604 and 204 is formed over the highlyflat semiconductor layer; therefore, coverage is good and shape defectsare not easily generated. Accordingly, defects such as leakage currentand a short can be prevented between the gate electrode layers 605 and205 formed over the gate insulating layers 604 and 204, respectively,and the element region. Thus, a semiconductor device having an NMOSstructure, a PMOS structure, or a CMOS structure of this embodiment modecan be a highly reliable semiconductor device in which defects such as ashort and leakage current between the gate electrode and thesemiconductor layer that are caused by a coverage defect of thesemiconductor layer with the gate insulating layer are prevented.

In FIG. 1B, the impurity region is shown by hatching and a blank space.This does not mean that the blank space is not doped with an impurityelement, but makes it intuitively understand that the concentrationdistribution of the impurity element in this region reflects the maskand the doping condition. It is to be noted that this is similar inother drawings of this specification, as well.

As the substrate 200 that is a substrate having an insulating surface, aglass substrate, a quartz substrate, a sapphire substrate, a ceramicsubstrate, a metal substrate over the surface of which an insulatinglayer is formed, or the like can be used.

As the insulating layer 201, the gate insulating layer 204, and theinsulating layer 206, silicon oxide, silicon nitride, siliconoxynitride, silicon nitride oxide, or the like can be used, which may beformed in a single layer or a stacked structure of two layers, threelayers, or the like. It is to be noted that, in this specification,silicon oxynitride refers to a substance in which the content of oxygenis higher than that of nitrogen, and can also be referred to as siliconoxide containing nitrogen. In the same manner, silicon nitride oxiderefers to a substance in which the content of nitrogen is higher thanthat of oxygen, and can also be referred to as silicon nitridecontaining oxygen.

In addition, as another material of the insulating layer 201, the gateinsulating layer 204, and the insulating layer 206, a material selectedfrom aluminum nitride, aluminum oxynitride in which the content ofoxygen is higher than that of nitrogen, aluminum nitride oxide oraluminum oxide in which the content of nitrogen is higher than that ofoxygen, diamond like carbon (DLC), nitrogen-containing carbon,polysilazane, and other substances containing an inorganic insulatingmaterial can be used. A material containing siloxane may also be used.Siloxane corresponds to a material containing the Si—O—Si bond. It is tobe noted that siloxane is composed of a skeleton structure formed by thebond of silicon (Si) and oxygen (O). As a substituent thereof, anorganic group containing at least hydrogen (for example, an alkyl groupor an aryl group) is used. Alternatively, a fluoro group may also beused as the substituent. Further alternatively, a fluoro group and anorganic group containing at least hydrogen may also be used as thesubstituent. In addition, an oxazole resin can be used, and for example,photo-curable type polybenzoxazole or the like can be used.

The insulating layer 201, the gate insulating layer 204, and theinsulating layer 206 can be formed by a sputtering method, a PVD(Physical Vapor Deposition) method, a low pressure CVD method (LPCVDmethod), or a CVD (Chemical Vapor Deposition) method such as a plasmaCVD method. Alternatively, a droplet discharging method by which apattern can be selectively formed, a printing method by which a patterncan be transferred or described (a method, such as a screen printingmethod or an offset printing method, by which a pattern is formed), orother methods such as a coating method such as a spin coating method, adipping method, a dispenser method, or the like can also be used.

An etching process for processing into a desired shape may employ eitherplasma etching (dry etching) or wet etching. In a case of processing alarge-sized substrate, plasma etching is suitable. As an etching gas, afluorine-based gas such as CF₄ or NF₃ or a chlorine-based gas such asCl₂ or BCl₃ is used, to which an inert gas such as He or Ar may beappropriately added. When an etching process by atmospheric pressuredischarge is employed, local electric discharge can also be realized,which does not require a mask layer to be formed over an entire surfaceof the substrate.

Alternatively, the gate insulating layer may be formed by performingplasma treatment on the semiconductor layer. By performance of plasmatreatment under a nitrogen atmosphere or an oxygen atmosphere, forexample, by performance of nitridation treatment or oxidizationtreatment on the surface and in the vicinity of the surface of thesemiconductor layer using silicon, a nitrogen plasma-treated layer or anoxygen plasma-treated layer can be formed. When oxidization treatment ornitridation treatment (or both of the oxidization treatment andnitridation treatment may be performed) is performed on the gateinsulating layer by plasma treatment, the surface of the gate insulatinglayer is modified, whereby a denser gate insulating layer can be formed.Accordingly, defects such as pinholes can be suppressed and acharacteristic or the like of the semiconductor device can be improved.

Plasma used for solid-phase oxidation treatment or solid-phasenitridation treatment by plasma treatment is preferable under thefollowing conditions: excited by microwave (typically, 2.45 GHz) at anelectron density of greater than or equal to 1×10¹¹ cm⁻³ and less thanor equal to 1×10¹³ cm⁻³ and at an electron temperature of greater thanor equal to 0.5 eV and less than or equal to 1.5 eV. The conditions arepreferred to form a dense insulating layer at a practical reaction ratesolid-phase oxidation treatment or solid-phase nitridation treatment at500° C. or less.

The oxidation of the surface of the semiconductor layer by this plasmatreatment is performed under an oxygen atmosphere (e.g., under anatmosphere containing oxygen (O₂) or dinitrogen monoxide (N₂O), and arare gas (containing at least one of He, Ne, Ar, Kr, and Xe), or underan atmosphere containing oxygen or dinitrogen monoxide, hydrogen (H₂),and a rare gas). The nitridation of the surface of the semiconductorlayer by this plasma treatment is performed under a nitrogen atmosphere(e.g., under an atmosphere containing nitrogen (N₂) and a rare gas(containing at least one of He, Ne, Ar, Kr, and Xe), under an atmospherecontaining nitrogen, hydrogen, and a rare gas, or under an atmospherecontaining NH₃ and a rare gas). As the rare gas, Ar can be used forexample. Further, a gas in which Ar and Kr are mixed may also be used.The plasma treatment includes oxidation treatment, nitridationtreatment, oxynitridation treatment, hydrogenation treatment, andsurface modification treatment performed on a semiconductor layer, aninsulating layer, and a conductive layer. By excitation of plasma withmicrowave introduction, plasma with a low electron temperature (lessthan or equal to 3 eV, preferably less than or equal to 1.5 eV) and highelectron density (greater than or equal to 1×10¹¹ cm⁻³) can be produced.With oxygen radicals (which may include OH radicals) and/or nitrogenradicals (which may include NH radicals) generated by this high-densityplasma, the surface of the semiconductor layer can be oxidized and/ornitrided. By mixture of a rare gas such as argon into the plasmatreatment gas, oxygen radicals or nitrogen radicals can be effectivelygenerated by excited species of the rare gas.

When a silicon layer is used as a typical example of the semiconductorlayer, the surface of the silicon layer is oxidized by plasma treatment,so that a dense oxide layer without distortion at the interface can beformed. Furthermore, by nitridation of the surface of the oxide layer byplasma treatment so that oxygen in the superficial layer portion isreplaced with nitrogen to form a nitride layer, the density of theinsulating layer can be further improved. Consequently, an insulatinglayer which is high in dielectric strength voltage can be formed.

However, when plasma treatment is performed in the present invention,the plasma treatment is performed under the condition where an electriccharacteristic of a transistor is not adversely affected.

Further, even after forming the substrate, the insulating layer, theinterlayer insulating layer, or other insulating layers, conductivelayers, and the like included in the semiconductor device, oxidationtreatment or nitridation treatment by plasma treatment may be performedon the surface of the substrate, the insulating layer, or the interlayerinsulating layer. By the oxidation treatment or the nitridationtreatment performed on the surface of the insulating layer by plasmatreatment, the surface of the insulating layer can be modified, so thatan insulating layer that is denser than an insulating layer formed by aCVD method or a sputtering method can be formed. Therefore, defects suchas pin holes can be suppressed, and the characteristics and the like ofthe semiconductor device can be improved. The above-described plasmatreatment can also be performed on conductive layers or the like such asa gate electrode layer, a source wiring layer, and a drain wiring layer.In that case, the surface of the layer or the vicinity of the surfacecan be nitrided or oxidized.

The semiconductor layer is preferably formed using a single-crystallinesemiconductor or a polycrystalline semiconductor. For example, thesemiconductor layer can be obtained by crystallizing a semiconductorlayer that is formed over an entire surface of the substrate by asputtering method, a plasma CVD method, or a low pressure CVD method.The semiconductor material is preferably silicon, and a silicongermanium semiconductor can also be used as well. Crystallization of thesemiconductor layer can be performed by a laser crystallization method,a thermal crystallization method using rapid thermal annealing (RTA) oran annealing furnace, a crystallization method using a metal elementthat promotes the crystallization, or a method combining them.

A p-type impurity may be injected into the semiconductor layer. As thep-type impurity, for example, boron may be used and added at aconcentration of approximately from 5×10¹⁵ atoms/cm³ to 1×10¹⁶atoms/cm³. The impurity is added to control the threshold voltage of atransistor, and the impurity effectively operates when it is added tothe channel formation regions 209 a and 209 b.

The wiring layer and the gate electrode layer included in the transistorcan be formed from a material selected from indium tin oxide (ITO),indium zinc oxide (IZO) in which zinc oxide (ZnO) is mixed with indiumoxide, a conductive material in which silicon oxide (SiO₂) is mixed withindium oxide, organoindium, organotin, indium oxide containing tungstenoxide, indium zinc oxide containing tungsten oxide, indium oxidecontaining titanium oxide, or indium tin oxide containing titaniumoxide; a metal such as tungsten (W), molybdenum (Mo), zirconium (Zr),hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr),cobalt (Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al),copper (Cu), or silver (Ag); an alloy of such metals; or metal nitridethereof.

A structure of the thin film transistor is not limited to that in thisembodiment mode, and the thin film transistor may have a single-gatestructure in which one channel formation region is formed, a double-gatestructure in which two channel formation regions are formed, or atriple-gate structure in which three channel formation regions areformed. A thin film transistor in the peripheral driver circuit regionmay have a single-gate structure, a double-gate structure, or atriple-gate structure.

Therefore, with the use of the present invention, a semiconductor layercan be isolated into a plurality of element regions without beingdivided into island shapes. Steps resulting from the edge portion of thesemiconductor layer are not generated, and thus a gate insulating layeris formed over a flat semiconductor layer, leading to improvement incoverage of the semiconductor layer with the gate insulating layer.Accordingly, the present invention can provide a highly reliablesemiconductor device in which defects such as a short and leakagecurrent between the gate electrode layer and the semiconductor layerthat are caused by coverage defect of the semiconductor layer with thegate insulating layer are prevented, and a manufacturing method of sucha semiconductor device. Hence, miniaturization and integration can befurther performed in a semiconductor device, and high performance of thesemiconductor device can be accomplished. In addition, because a defectcaused by a shape defect of such a film can be reduced, in amanufacturing process, a semiconductor device can be produced with goodyield.

Embodiment Mode 2

In this embodiment mode, as a highly reliable semiconductor device inwhich defects such as a short and leakage current between an electrodelayer and a semiconductor layer that are caused by a coverage defect ofa semiconductor layer with an insulating layer are prevented, an exampleof a nonvolatile semiconductor storage device will be described withreference to the drawings.

Features of a nonvolatile storage element lie in that its structure issimilar to that of a MOSFET (Metal Oxide Semiconductor Field EffectTransistor) and a region capable of accumulating charges for a longperiod of time is provided over a channel formation region. The chargeaccumulation region is formed over an insulating layer and is insulatedand isolated from the surroundings; therefore, it is also referred to asa floating gate electrode layer. Because the floating gate electrodelayer has a function to accumulate charges, it is also referred to as acharge accumulation layer. In this specification, this chargeaccumulation region including the floating gate electrode layer ismainly referred to as a charge accumulation layer. A control gateelectrode layer is provided over the floating gate electrode layer withan insulating layer interposed therebetween.

In a so-called floating gate type nonvolatile semiconductor storagedevice having such a structure, charges are accumulated and releasedin/from the charge accumulation layer by voltage applied to the controlgate electrode layer. In other words, the so-called floating gate typenonvolatile semiconductor memory device has a mechanism of storing databy injection and release of charges stored in the charge accumulationlayer. Specifically, the injection of charges into the chargeaccumulation layer and the release of charges from the chargeaccumulation layer are carried out by application of high voltagebetween the control gate electrode layer and a semiconductor layer inwhich a channel formation region is formed. Here, Fowler-Nordheim (F-N)tunneling current (in the case of NAND type) or hot electrons (in thecase of NOR-type) is said to flow in the insulating layer over thechannel formation region. Thus, the insulating layer is also called atunnel insulating layer.

FIGS. 2A to 2C show an example of a semiconductor device that is anonvolatile semiconductor storage device of this embodiment mode. FIG.2A is a top view, FIG. 2B is a cross-sectional view taken along a lineE-F in FIG. 2A, and FIG. 2C is a cross-sectional view taken along a lineG-H in FIG. 2A.

A memory element 270 that is a nonvolatile memory element and aninterlayer insulating layer 258 are formed over a substrate 250 overwhich an insulating layer 251 serving as a base film of a semiconductorlayer is formed. The memory element 270 includes an element regionhaving high-concentration impurity regions 261 a and 261 b,low-concentration impurity regions 262 a and 262 b, and a channelformation region 253, a first insulating layer 254, a chargeaccumulation layer 271, a second insulating layer 256, a control gateelectrode layer 272, and wiring layers 259 a and 259 b. Elementisolation regions 252 a and 252 b are formed to be in contact with theelement region (see FIGS. 2A to 2C).

An impurity element that imparts n-type conductivity (phosphorus (P),arsenic (As), or the like) or an impurity element that imparts p-typeconductivity (for example, boron (B), aluminum (Al), gallium (Ga), orthe like) is included as an impurity element that imparts oneconductivity type in the high-concentration impurity regions 261 a and261 b and the low-concentration impurity regions 262 a and 262 b. Thehigh-concentration impurity regions 261 a and 261 b are regions servingas a source and a drain in the memory element.

In the semiconductor layer, the element region having thehigh-concentration impurity regions 261 a and 261 b, thelow-concentration impurity regions 262 a and 262 b, and the channelformation region 253 is electrically isolated from other memory elementsby an element isolation region 252 (252 a, 252 b, 252 c, and 252 d)surrounding its periphery.

The element isolation region is formed by selective addition of a firstimpurity element that does not contribute to conductivity and a secondimpurity element that imparts an opposite conductivity type to that of asource region and a drain region in the element region in order toelectrically isolate elements from each other in one semiconductorlayer.

As the first impurity element that does not contribute to conductivity,an impurity element of at least one or more kinds of oxygen, nitrogen,and carbon can be used. The element isolation region to which the firstimpurity element is added, conductivity is lowered by mixture of thefirst impurity element that does not contribute to conductivity, andresistance of the element isolation region is increased because itscrystallinity is lowered by a physical impact (it can also be referredto as a so-called sputtering effect) on the semiconductor layer atadding. In the element isolation region with the increased resistance,electron field-effect mobility is also lowered, and accordingly,elements can be electrically isolated from each other. On the otherhand, in a region to which an impurity element is not added, electronfield-effect mobility that is high enough to be able to serve as anelement is kept, and accordingly, the region can be used as an elementregion.

The element region has a source region, a drain region, and a channelformation region. The source region and the drain region are impurityregions having one conductivity type (for example, n-type impurityregions or p-type impurity regions). An impurity element that imparts anopposite conductivity type to that of the source region and the drainregion in the element region is added to the element isolation region,whereby the element isolation region is made to be an impurity regionhaving an opposite conductivity type to that of the source region andthe drain region in the adjacent element region. That is, in a casewhere the source region and the drain region in the element region aren-type impurity regions, the adjacent element isolation region may beformed as a p-type impurity region. Similarly, in a case where thesource region and the drain region in the element region are p-typeimpurity regions, the adjacent element isolation region may be formed asan n-type impurity region. The element region and the element isolationregion that are adjacent to each other form a PN junction. Accordingly,the element regions can be further insulated and isolated from eachother by the element isolation region provided between the elementregions.

One feature of the present invention is that one semiconductor layer isisolated into a plurality of element regions in the manner thatresistance of the element isolation region by which the element regionsare insulated and isolated from each other is increased by addition ofthe first impurity element that does not contribute to conductivity, andfurther, a PN junction is formed in a position where the element regionand the element isolation region are in contact with each other byaddition of the second impurity element that imparts an oppositeconductivity type to that of the source region and the drain region inthe element region. By the present invention, the element regions can beisolated from each other by an effect caused by each of the firstimpurity element and the second impurity element. Thus, a higher effectof insulation and isolation of the element can be obtained.

FIGS. 4A to 4C show a case where a plurality of memory elements isformed. Because the element isolation region 252 (252 a, 252 b, 252 c,and 252 d) is provided to be in contact with the n-typehigh-concentration impurity regions 261 a and 261 b, the elementisolation region 252 may be formed as a p-type impurity region byaddition of an impurity element that imparts p-type conductivity (forexample, boron (B), aluminum (Al), gallium (Ga), or the like) as asecond impurity element that imparts an opposite conductivity type tothat of the source region and the drain region in the element region.

The addition (introduction) of the first impurity element and the secondimpurity element in forming the element isolation region can beperformed by an ion implantation method, an (ion) doping method, or thelike.

The resistivity of the element isolation region is preferably greaterthan or equal to 1×10¹⁰ Ω·cm, and the concentration of the firstimpurity element such as oxygen, nitrogen, or carbon is preferablygreater than or equal to 1×10²⁰ Ω·cm⁻³ and less than 4×10²² Ω·cm⁻³.

Crystallinity of the element isolation region is lowered by addition ofthe impurity element; therefore, it can be said that the elementisolation region is made to be amorphous. On the other hand, because theelement region is a crystalline semiconductor layer, in a case where asemiconductor element is formed in the element region, crystallinity ofthe channel formation region is higher than that of the elementisolation region, and high electron field-effect mobility can beobtained as a semiconductor element. As the impurity element added tothe element isolation region, a rare gas element such as argon (Ar),neon (Ne), krypton (Kr), or xenon (Xe) may be used. By further additionof such a rare gas element that is an element having comparatively highmass as well as oxygen, nitrogen, and carbon, a physical impact on thesemiconductor layer can be increased, whereby crystallinity of theelement isolation region can be lowered more effectively.

In FIG. 2C, a control gate electrode layer 272 is formed to extend overthe channel formation region 253 and the element isolation regions 252 cand 252 d in the semiconductor layer, with the first insulating layer254, the charge accumulation layer 271, and the second insulating layer256 interposed between the control gate electrode layer 272 and thesemiconductor layer. In the present invention, the element isolationregion and the element region are provided in the continuoussemiconductor layer; therefore, the element isolation regions 252 c and252 d and the element region, which is the channel formation region 253,are contiguous. Thus, the surface thereof has high flatness and no steepstep.

The first insulating layer 254 is formed over the highly flatsemiconductor layer; therefore, coverage is good and shape defects arenot easily generated. Accordingly, defects such as leakage current and ashort can be prevented between the charge accumulation layer 271 formedover the first insulating layer 254 and channel formation region 253.Thus, a semiconductor device that is a nonvolatile semiconductor storagedevice of this embodiment mode can be a highly reliable semiconductordevice in which defects such as a short and leakage current between thecharge accumulation layer and the semiconductor layer that are caused bya coverage defect of the semiconductor layer with the first insulatinglayer 254 are prevented.

In FIGS. 2A to 2C, an example is shown in which the element region inthe semiconductor layer is narrower than the charge accumulation layer271 in the line G-H direction and wider than that of the control gateelectrode layer 272 in the line E-F direction. However, the presentinvention is not limited thereto. FIGS. 26A to 26C and FIGS. 27A to 27Ceach show the other combinations of the sizes of the element region, thecharge accumulation layer, and the control gate electrode layer. FIGS.26A to 26C and FIGS. 27A to 27C are similar to FIGS. 2A to 2C other thanthe charge accumulation layer and the control gate electrode layer;therefore, the same reference numerals as those in FIGS. 2A to 2C areused, and explanation will be omitted.

In a memory element 290 in FIGS. 26A to 26C, the width of an elementregion in a semiconductor layer is almost the same as that of a chargeaccumulation layer 291 in the line G-H direction, and is wider than thatof a control gate electrode layer 292 in the line E-F direction.Therefore, in FIG. 26B, the edge portion of the charge accumulationlayer 291 and the edge portion of the control gate electrode layer 292roughly coincide with each other with a second insulating layer 256interposed between the charge accumulation layer 291 and the controlgate electrode layer 292, and in FIG. 26C, the edge portion of a channelformation region 253 in the element region and the edge portion of thecharge accumulation layer 291 roughly coincide with each other with afirst insulating layer 254 interposed between the channel formationregion 253 and the charge accumulation layer 291. Further, a secondimpurity element is selectively added to an element isolation region inFIGS. 26A to 26C, and the element isolation region includes firstelement isolation regions 293 a and 293 b and second element isolationregion 294 a and 294 b. An example is shown in which the second impurityelement that imparts an opposite conductivity type to that of the sourceregion and the drain region in the element region is selectively addedto the first element isolation regions 293 a and 293 b, and only thefirst impurity element is added to the second element isolation region294 a and 294 b. As described above, in the present invention, the firstimpurity element and the second impurity element are included in theelement isolation region. However, the first impurity element and thesecond impurity element may be selectively added, and at least one ofthe first impurity element and the second impurity element may be added.Of course, one of the first impurity element and the second impurityelement can be added to the entire element isolation region and theother can be selectively added.

In a memory element 280 in FIGS. 27A to 27C, an element region in asemiconductor layer is wider than a charge accumulation layer 281 in theline G-H direction, and wider than a control gate electrode layer 282 inthe line E-F direction. Therefore, in FIG. 27B, the edge portion of thecharge accumulation layer 281 is positioned on the inner side than theedge portion of the control gate electrode layer 282 with a secondinsulating layer 256 interposed between the charge accumulation layer281 and the control gate electrode layer 282. In FIG. 27C, the edgeportion of a channel formation region 253 in the element region ispositioned on the outer side than the edge portion of the chargeaccumulation layer 281 with a first insulating layer 254 interposedbetween the channel formation region 253 and the charge accumulationlayer 281. Similarly to FIGS. 26A to 26C, the second impurity element isselectively added to an element isolation region in FIGS. 27A to 27C,and the first element isolation regions 284 a and 284 b and secondelement isolation regions 283 a and 283 b are formed. In FIGS. 27A to27C, a second impurity element is selectively added to the secondelement isolation regions 283 a and 283 b, and a first impurity elementis added to the first element isolation regions 284 a and 284 b and thesecond element isolation regions 283 a and 283 b. In such a manner, theregion to which the second impurity element that imparts an oppositeconductivity type to that of the source region and the drain region inthe element region is added may be in the vicinity of the surface of thesemiconductor layer or in the vicinity of the substrate.

In such a manner, by a combination of the sizes of the element region,the charge accumulation layer, and the control gate electrode layer,capacitance to be formed in the second insulating layer between thecharge accumulation layer and the control gate electrode layer andcapacitance to be formed in the first insulating layer 254 between thecharge accumulation layer and the semiconductor layer can be controlled.Accordingly, a voltage value to be applied can also be controlled.

As the interlayer insulating layer 258, silicon oxide, silicon nitride,silicon oxynitride, silicon nitride oxide, or the like can be used,which may be formed in a single layer or a stacked structure of twolayers, three layers, or the like. It is to be noted that, in thisspecification, silicon oxynitride refers to a substance in which thecontent of oxygen is higher than that of nitrogen, and can also bereferred to as silicon oxide containing nitrogen. In the same manner,silicon nitride oxide refers to a substance in which the content ofnitrogen is higher than that of oxygen, and can also be referred to assilicon nitride containing oxygen.

In addition, as another material of the interlayer insulating layer 258,a material selected from aluminum nitride, aluminum oxynitride in whichthe content of oxygen is higher than that of nitrogen, aluminum nitrideoxide or aluminum oxide in which the content of nitrogen is higher thanthat of oxygen, diamond like carbon (DLC), nitrogen-containing carbon,polysilazane, and other substances containing an inorganic insulatingmaterial can be used. A material containing siloxane may also be used.Siloxane corresponds to a material containing the Si—O—Si bond. It is tobe noted that siloxane is composed of a skeleton structure formed by thebond of silicon (Si) and oxygen (O). As a substituent thereof, anorganic group containing at least hydrogen (for example, an alkyl groupor an aryl group) is used. Alternatively, a fluoro group may also beused as the substituent. Further alternatively, a fluoro group and anorganic group containing at least hydrogen may also be used as thesubstituent. In addition, an oxazole resin can be used, and for example,photo-curable type polybenzoxazole or the like can be used.

The interlayer insulating layer 258 can be formed by a sputteringmethod, a PVD (Physical Vapor Deposition) method, a low pressure CVDmethod (LPCVD method), or a CVD (Chemical Vapor Deposition) method suchas a plasma CVD method. Alternatively, a droplet discharging method bywhich a pattern can be selectively formed, a printing method by which apattern can be transferred or described (a method, such as a screenprinting method or an offset printing method, by which a pattern isformed), or other methods such as a coating method such as a spincoating method, a dipping method, a dispenser method, or the like canalso be used.

An etching process for processing into a desired shape may employ eitherplasma etching (dry etching) or wet etching. In a case of processing alarge-sized substrate, plasma etching is suitable. As an etching gas, afluorine-based gas such as CF₄ or NF₃ or a chlorine-based gas such asCl₂ or BCl₃ is used, to which an inert gas such as He or Ar may beappropriately added. When an etching process by atmospheric pressuredischarge is employed, local electric discharge can also be realized,which does not require a mask layer to be formed over an entire surfaceof the substrate.

The semiconductor layer is preferably formed using a single-crystallinesemiconductor or a polycrystalline semiconductor. For example, thesemiconductor layer can be obtained by crystallizing a semiconductorlayer that is formed over an entire surface of the substrate by asputtering method, a plasma CVD method, or a low pressure CVD method.The semiconductor material is preferably silicon, and a silicongermanium semiconductor can also be used as well. Crystallization of thesemiconductor layer can be performed by a laser crystallization method,a thermal crystallization method using rapid thermal annealing (RTA) oran annealing furnace, a crystallization method using a metal elementthat promotes the crystallization, or a method combining them.

A p-type impurity may be injected into the semiconductor layer. As thep-type impurity, for example, boron may be used and added at aconcentration of approximately from 5×10¹⁵ atoms/cm³ to 1×10¹⁶atoms/cm³. The impurity is added to control the threshold voltage of thesemiconductor element, and the impurity effectively operates when it isadded to the channel formation region 253.

The first insulating layer 254 may be formed using silicon oxide or astacked structure of silicon oxide and silicon nitride. The firstinsulating layer 254 may be formed by deposition of an insulating layerby a plasma CVD method or a low pressure CVD method; however, it ispreferably formed by solid-phase oxidation or solid-phase nitridationusing plasma treatment. This is because the insulating layer formed byoxidization or nitridation of a semiconductor layer (typically, asilicon layer) by plasma treatment is dense and has high dielectricstrength voltage and high reliability. Since the first insulating layer254 is used as a tunnel insulating layer for injecting charges into thecharge accumulation layers 271, 281, and 291, it is preferable that theinsulating layer is dense and has high dielectric strength voltage andhigh reliability. This first insulating layer 254 is preferably formedat a thickness of from 1 to 20 nm, preferably from 3 to 6 nm. Forexample, when the gate length is 600 nm, the first insulating layer 254can be formed at a thickness of from 3 to 6 nm.

Plasma used for solid-phase oxidation treatment or solid-phasenitridation treatment by plasma treatment is preferable under thefollowing conditions: excited by microwave (typically, 2.45 GHz) at anelectron density of greater than or equal to 1×10¹¹ cm⁻³ and less thanor equal to 1×10¹³ cm⁻³ and at an electron temperature of greater thanor equal to 0.5 eV and less than or equal to 1.5 eV. The conditions arepreferred to form a dense insulating layer at a practical reaction ratesolid-phase oxidation treatment or solid-phase nitridation treatment at500° C. or less.

The oxidation of the surface of the semiconductor layer by this plasmatreatment is performed under an oxygen atmosphere (e.g., under anatmosphere containing oxygen (O₂) or dinitrogen monoxide (N₂O), and arare gas (containing at least one of He, Ne, Ar, Kr, and Xe), or underan atmosphere containing oxygen or dinitrogen monoxide, hydrogen (H₂),and a rare gas). The nitridation of the surface of the semiconductorlayer by this plasma treatment is performed under a nitrogen atmosphere(e.g., under an atmosphere containing nitrogen (N₂) and a rare gas(containing at least one of He, Ne, Ar, Kr, and Xe), under an atmospherecontaining nitrogen, hydrogen, and a rare gas, or under an atmospherecontaining NH₃ and a rare gas). As the rare gas, Ar can be used forexample. Further, a gas in which Ar and Kr are mixed may also be used.The plasma treatment includes oxidation treatment, nitridationtreatment, oxynitridation treatment, hydrogenation treatment, andsurface modification treatment performed on a semiconductor layer, aninsulating layer, and a conductive layer. By excitation of plasma withmicrowave introduction, plasma with a low electron temperature (lessthan or equal to 3 eV, preferably less than or equal to 1.5 eV) and highelectron density (greater than or equal to 1×10¹¹ cm⁻³) can be produced.With oxygen radicals (which may include OH radicals) and/or nitrogenradicals (which may include NH radicals) generated by this high-densityplasma, the surface of the semiconductor layer can be oxidized and/ornitrided. By mixture of a rare gas such as argon into the plasmatreatment gas, oxygen radicals or nitrogen radicals can be effectivelygenerated by excited species of the rare gas.

In FIGS. 2A to 2C, as a preferable example of the first insulating layer254 formed by plasma treatment, the following steps are conducted:forming a silicon oxide layer at a thickness of 3 to 6 nm over thesemiconductor layer by plasma treatment under an oxygen atmosphere, andforming a nitrogen plasma-treated layer over the surface of the siliconoxide layer by plasma treatment under a nitrogen atmosphere.Specifically, the silicon oxide layer is formed at a thickness of 3 to 6nm over the semiconductor layer by plasma treatment under an oxygenatmosphere. Subsequently, by conduction of plasma treatment under anitrogen atmosphere, the nitrogen plasma-treated layer containing a highconcentration of nitrogen is provided over the surface of the siliconoxide layer or in the vicinity of the surface. It is to be noted thatthe vicinity of the surface indicates a depth of approximately 0.5 to1.5 nm from the surface of the silicon oxide layer. For example, byplasma treatment under a nitrogen atmosphere, a structure is obtained inwhich the silicon oxide layer contains 20 to 50 atomic % nitrogen to adepth of about 1 nm from the surface.

When a silicon layer is used as a typical example of the semiconductorlayer, the surface of the silicon layer is oxidized by plasma treatment,so that a dense oxide layer without distortion at the interface can beformed. Furthermore, by nitridation of the surface of the oxide layer byplasma treatment so that oxygen in the superficial layer portion isreplaced with nitrogen to form a nitride layer, the density of theinsulating layer can be further improved. Consequently, an insulatinglayer which is high in dielectric strength voltage can be formed.

In any case, by solid-phase oxidation treatment or solid-phasenitridation treatment by plasma treatment described above, an insulatinglayer that is similar to a thermal oxide film formed at a temperature of950 to 1050° C. can be obtained even when a glass substrate having aheat resistant temperature of less than or equal to 700° C. is used.That is, a highly reliable tunnel insulating layer can be formed as atunnel insulating layer of a nonvolatile memory element.

Each of the charge accumulation layers 271, 281, and 291 is formed overthe first insulating layer 254. These charge accumulation layers 271,281, and 291 may be provided in a single layer or a stack of a pluralityof layers.

The charge accumulation layers 271, 281, and 291 can be formed using,typically, silicon, a silicon compound, germanium, or a germaniumcompound as a semiconductor material forming the charge accumulationlayers 271, 281, and 291. As a silicon compound, silicon nitride,silicon nitride oxide, silicon carbide, silicon germanium containinggermanium at a concentration of greater than or equal to 10 atomic %,metal nitride, metal oxide, or the like can be used. Silicon germaniumis a typical example of a germanium compound, and in this case, it ispreferable that germanium be contained at a concentration of greaterthan or equal to 10 atomic % with respect to silicon.

The charge accumulation layer serving as a floating gate is applied to anonvolatile semiconductor storage device according to the presentinvention for charge accumulation. However, other materials can beapplied as long as the similar function is provided. For example, aternary system semiconductor including germanium may be used. Inaddition, the semiconductor material may be hydrogenated. Further, as alayer having a function as a charge accumulation layer of a nonvolatilememory element, the charge accumulation layer can be replaced with anoxide or a nitride of the germanium or a germanium compound.

Further, metal nitride or metal oxide can be used as a material formingthe charge accumulation layers 271, 281, and 291. As metal nitride,tantalum nitride, tungsten nitride, molybdenum nitride, titaniumnitride, or the like can be used. As metal oxide, tantalum oxide,titanium oxide, tin oxide, or the like can be used.

Further, the charge accumulation layers 271, 281, and 291 may be formedusing a stacked structure of the material as described above. When alayer of silicon or a silicon compound, or metal nitride or metal oxideas described above is provided on the upper layer side of the layerformed using germanium or a germanium compound, the layer can be used asa barrier layer for water resistance or chemical resistance in themanufacturing process. Therefore, the substrate can be easily handled ina photolithography step, an etching step, or a cleaning step, wherebyproductivity can be improved. In other words, the charge accumulationlayer can be easily processed.

The second insulating layer 256 is formed using a single layer or aplurality of layers of silicon oxide, silicon oxynitride (SiO_(x)N_(y)(x>y>0)), silicon nitride (SiN_(x)), silicon nitride oxide (SiN_(x)O_(y)(x>y>0)), and the like by a low pressure CVD method, a plasma CVDmethod, or the like. Alternatively, the second insulating layer 256 maybe formed using aluminum oxide (AlOx), hafnium oxide (HfOx), or tantalumoxide (TaOx). The second insulating layer 256 is formed at a thicknessof from 1 to 20 nm, preferably from 5 to 10 nm. For example, a siliconnitride layer is deposited at a thickness of 3 nm, and a silicon oxidelayer is deposited thereover at a thickness of 5 nm, to be used.Further, nitride films may also be formed by plasma treatment beingperformed on surfaces of the charge accumulation layers 271, 281, and291 to perform nitridation treatment on the surfaces of the the chargeaccumulation layers 271, 281, and 291 (e.g., silicon nitride in the casewhere silicon is used for the charge accumulation layers 271, 281, and291). In any case, one or both of a side of the first insulating layer254 and a side of the second insulating layer 256, which are in contactwith the charge accumulation layers 271, 281, and 291, are nitridefilms; thus, the charge accumulation layers 271, 281, and 291 can beprevented from being oxidized.

The control gate electrode layers 272, 282, and 292 are preferablyformed using a metal selected from tantalum (Ta), tungsten (W), titanium(Ti), molybdenum (Mo), chromium (Cr), niobium (Nb), and the like, or analloy material or a compound material containing the metal as its maincomponent. Alternatively, polycrystalline silicon to which an impurityelement such as phosphorus is added can be used. Further alternatively,a staked structure of one layer or a plurality of layers of a metalnitride layer and a metal layer described above may also be formed asthe control gate electrode layers 272, 282, and 292. As the metalnitride, tungsten nitride, molybdenum nitride, or titanium nitride canbe used. By the metal nitride layer being provided, adhesion to thesecond insulating layer 256 can be improved, and the control gateelectrode layers 272, 282, and 292 can be prevented from being peeledfrom the second insulating layer 256. When metal nitride such astantalum nitride having a high work function is used for the controlgate electrode layers 272, 282, and 292, the first insulating layer 254can be formed to be thick by the synergistic effect with the secondinsulating layer 256.

The wiring layers 259 a and 259 b can be formed from a material selectedfrom indium tin oxide (ITO), indium zinc oxide (IZO) in which zinc oxide(ZnO) is mixed with indium oxide, a conductive material in which siliconoxide (SiO₂) is mixed with indium oxide, organoindium, organotin, indiumoxide containing tungsten oxide, indium zinc oxide containing tungstenoxide, indium oxide containing titanium oxide, or indium tin oxidecontaining titanium oxide; a metal such as tungsten (W), molybdenum(Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum(Ta), chromium (Cr), cobalt (Co), nickel (Ni), titanium (Ti), platinum(Pt), aluminum (Al), copper (Cu), or silver (Ag); an alloy of suchmetals; or metal nitride thereof.

There are the following methods for injecting electrons into the chargeaccumulation layer: a method utilizing hot electrons and a methodutilizing F-N tunneling current. In the case of utilizing hot electrons,a positive voltage is applied to the control gate electrode layer and ahigh voltage is applied to a drain to generate hot electrons. Thus, thehot electrons can be injected into the charge accumulation layer. In thecase of utilizing F-N tunneling current, a positive voltage is appliedto the control gate electrode layer so that electrons are injected intothe charge accumulation layer from the semiconductor layer by using F-Ntunneling current.

As examples of a semiconductor device using the present invention,various modes of nonvolatile semiconductor storages having nonvolatilememory elements can be given. FIG. 12 shows an exemplary equivalentcircuit of a nonvolatile memory cell array. A memory cell MS01 whichstores data of 1 bit includes a selection transistor S01 and anonvolatile memory element M01. The selection transistor S01 isconnected in series between a bit line BL0 and the nonvolatile memoryelement M01, and a gate of the selection transistor S01 is connected toa word line WL1. A gate of the nonvolatile memory element M01 isconnected to a word line WL11. When writing data into the nonvolatilememory element M01, the word line WL1 and the bit line BL0 are set at Hlevel, a bit line BL1 is set at L level, and a high voltage is appliedto the word line WL11, so that charges are accumulated in the chargeaccumulation layer as described above. When deleting data, the word lineWL1 and the bit line BL0 may be set at H level, and a high voltage ofnegative polarity may be applied to the word line WL11.

In this memory cell MS01, when the selection transistor S01 and thenonvolatile memory element M01 are formed using element regions 30 and32 respectively which are formed by isolating a semiconductor layerformed continuously over an insulating surface by providing elementisolation regions to which an impurity element is added, it is possibleto prevent mutual interference with other selection transistors ornonvolatile memory elements. In addition, since both of the selectiontransistor S01 and the nonvolatile memory element M01 included in thememory cell MS01 are n-channel transistors, when the two elements areformed using one element region, a wiring for connecting the twoelements can be omitted.

FIG. 13 shows an equivalent circuit of a NOR-type memory cell array inwhich nonvolatile memory elements are connected to a bit line. In thismemory cell array, word lines WL and bit lines BL are disposed tointersect each other, and a nonvolatile memory clement is disposed ateach intersection portion. In the NOR-type memory cell array, drains ofthe individual nonvolatile memory elements are connected to the bit lineBL, and sources of the nonvolatile memory elements are commonlyconnected to the source line SL.

In this case also, when the nonvolatile memory element M01 in the memorycell MS01 is formed using an element region 32 which is formed byisolating a semiconductor layer formed continuously over an insulatingsurface by providing element isolation regions to which an impurityelement is added, it is possible to prevent mutual interference withother nonvolatile memory elements without dividing the semiconductorlayer into a plurality of island-shaped semiconductor layers. Further,when a plurality of nonvolatile memory elements (e.g., M01 to M23 shownin FIG. 13) is regarded as one block, and the nonvolatile memoryelements in one block are formed using element regions which are formedby isolating a semiconductor layer formed continuously over aninsulating surface by providing element isolation regions to which animpurity element is added, a deletion operation can be conduced perblock.

The operation of the NOR-type memory cell array is as follows. In datawriting, the source line SL is set at 0 V, a high voltage is applied tothe word line WL which is selected to write data, and a potentialcorresponding to the data of “0” or “1” is applied to the bit line BL.For example, an H-level potential corresponding to “0” or an L-levelpotential corresponding to “1” is applied to the bit line BL. In thenonvolatile memory element which has received an H-level potential to bewritten the data of “0”, hot electrons are generated in the vicinity ofthe drain and then injected into the charge accumulation layer. Inwriting the data of “1”, such electron injection does not occur.

In the memory cell which has received the data of “0”, hot electrons,which are generated in the vicinity of the drain due to a strongtransverse electric field between the drain and the source, are injectedinto the charge accumulation layer. The consequent state in which thethreshold voltage is increased with the electrons injected into thecharge accumulation layer corresponds to “0”. When writing the data of“1”, hot electrons are not generated and a state that the thresholdvoltage remains low without electrons injected into the chargeaccumulation layer, i.e., a deleted state is retained.

When deleting data, a positive voltage of about 10 V is applied to thesource line SL, and the bit line BL is set in a floating state. Then, byapplying a high voltage of negative polarity to the word line WL(applying a high voltage of negative polarity to the control gate),electrons are extracted from the charge accumulation layer. Accordingly,a deleted state with the data of “1” results.

The data reading is conducted through the steps of: setting the sourceline SL at 0 V, setting the bit line BL at about 0.8 V, applying areading voltage which is set at an intermediate value between thethreshold voltages of the data “0” and “1” to the selected word line WL,and judging the presence of a current drawn into the nonvolatile memoryelement, using a sense amplifier which is connected to the bit line BL.

FIG. 14 shows an equivalent circuit of a NAND-type memory cell array. Abit line BL is connected to a NAND-type cell NS1 which has a pluralityof nonvolatile memory elements connected in series. A plurality ofNAND-type cells forms one block BLK. A block BLK1 shown in FIG. 14 has32 word lines (word lines WL0 to WL31). Nonvolatile memory elementspositioned in the same row as the block BLK1 are commonly connected tothe word lines of the corresponding row.

In this case, since selection transistors S1 and S2 and nonvolatilememory elements M0 to M31 are connected in series, these elements may beformed together by using one semiconductor layer 34. Accordingly, awiring for connecting the nonvolatile memory elements can be omitted,and the degree of integration can be increased. Further, isolation ofthe adjacent NAND-type cells can be conducted easily. It is alsopossible to separately form a semiconductor layer 36 of the selectiontransistors S1 and S2 and a semiconductor layer 38 of the NAND-typecell. When conducting a deletion operation by which charges areextracted from the charge accumulation layers of the nonvolatile memoryelements M0 to M31, the deletion operation can be conducted perNAND-type cell. In addition, it is also possible to form the nonvolatilememory elements which are commonly connected to one word line (e.g., inthe row of M30) by using one semiconductor layer 40.

The writing operation is conducted after setting the NAND-type cell NS1to a deleted state, i.e., the state in which the threshold voltage ofeach nonvolatile memory element in the NAND-type cell NS1 is set at anegative value. Writing is conducted sequentially starting from thenonvolatile memory element M0 on the source line SL side. Data writinginto the nonvolatile memory element M0 is exemplarily described below.

FIG. 24A shows the case of writing “0”. The selection transistor S2 isturned on by applying, for example, Vcc (the power supply voltage) to aselection gate line SG2, and the bit line BL is set at 0 V (the groundvoltage). The selection transistor S1 is turned off by setting aselection gate line SG1 at 0 V. Next, a word line WL0 connected to thenonvolatile memory element M0 is set at a high voltage of Vpgm (about 20V), and the other word lines are set at an intermediate voltage of Vpass(about 10 V). Since the voltage of the bit line BL is 0 V, the potentialof the channel formation region of the selected nonvolatile memoryelement M0 is also 0 V. Thus, there is a big potential differencebetween the word line WL0 and the channel formation region of thenonvolatile memory element M0, and therefore, electrons are injectedinto the charge accumulation layer of the nonvolatile memory element M0due to F-N tunnel current as described above. Accordingly, the thresholdvoltage of the nonvolatile memory element M0 has a positive value (thestate in which “0” is written).

On the other hand, in the case of writing “1”, the bit line BL is setat, for example, Vcc (the power supply voltage) as shown in FIG. 24B.Since the selection gate line SG2 has a voltage of Vcc, the selectiontransistor 52 is turned off when the gate voltage thereof is at Vth (thethreshold voltage of the selection transistor S2)>Vcc. Therefore, thechannel formation region of the nonvolatile memory element M0 is broughtinto a floating state. Next, when a high voltage of Vpgm (20 V) isapplied to the word line WL0 and an intermediate voltage of Vpass (10 V)is applied to the other word lines, the voltage of the channel formationregion of the nonvolatile memory element M0 increases from Vcc-Vth to,for example, about 8 V by the capacitive coupling of each word line andthe channel formation region. Although the voltage of the channelformation region is increased, there is a small potential differencebetween the word line WL0 and the channel formation region of thenonvolatile memory element M0 unlike the case of writing “0”. Therefore,electron injection into the charge accumulation layer of the nonvolatilememory element M0 due to F-N tunnel current does not occur. Thus, thethreshold voltage of the nonvolatile memory element M01 is kept at anegative value (the state in which “1” is written).

In the case of conducting a deletion operation, as shown in FIG. 25A, ahigh voltage of negative polarity (Vers) is applied to a selected wordline (WL0), a voltage Von (for example, 3 V) is applied to the wordlines WL of the non-selected nonvolatile memory elements, the selectiongate line SG1, and the selection gate line SG2, and an open-voltageVopen (0V) is applied to the bit line BL and the source line SL. Then,electrons in the charge accumulation layer of the selected nonvolatilememory element can be released as described in the above embodimentmode. As a result, the threshold voltage of the selected nonvolatilememory element shifts in the negative direction.

In the reading operation shown in FIG. 25B, the word line WL0 connectedto the nonvolatile memory element M0 which is selected to read out datais set at a voltage of Vr (e.g., 0 V), while the word lines WL1 to WL31connected to the non-selected nonvolatile memory elements and theselection gate lines SG1 and SG2 are set at an intermediate voltage ofVread which is a little higher than the power supply voltage. That is,as shown in FIG. 13, the nonvolatile memory elements other than theselected nonvolatile memory clement serve as transfer transistors.Accordingly, it is detected whether a current is flowing into thenonvolatile memory element M0 which is selected to read out data. Thatis, when data stored in the nonvolatile memory element M0 is “0”, thenonvolatile memory element M0 is off; therefore, the bit line BL is notdischarged. On the other hand, when data stored in the nonvolatilememory element M0 is “1”, the nonvolatile memory element M0 is on;therefore, the bit line BL is discharged.

FIG. 19 shows an example of a circuit block diagram of a nonvolatilesemiconductor storage device. In the nonvolatile semiconductor storagedevice, a memory cell array 52 and a peripheral circuit 54 are formedover the same substrate. The memory cell array 52 has the configurationshown in FIG. 12, 13, or 14. The peripheral circuit 54 has the followingconfiguration.

A row decoder 62 for selecting word lines and a column decoder 64 forselecting bit lines are provided around the memory cell array 52. Anaddress is transmitted to a control circuit 58 through an address buffer56, and an internal row address signal and an internal column addresssignal are transmitted to the row decoder 62 and the column decoder 64respectively.

In order to write or delete data, a potential obtained by boosting thepower supply potential is used. Therefore, a booster circuit 60 which iscontrolled by the control circuit 58 according to the operation mode isprovided. The output of the booster circuit 60 is supplied to word linesWL and bit lines BL through the row decoder 62 and the column decoder 64respectively. Data output from the column decoder 64 is input to a senseamplifier 66. Data read out by the sense amplifier 66 is held in a databuffer 68, and the data is randomly accessed by the control of thecontrol circuit 58. Then, the accessed data is output through a datainput/output buffer 70. Meanwhile, data to be written is, after beinginput through the data input/output buffer 70, once held in the databuffer 68, and then transferred to the column decoder 64 by the controlof the control circuit 58.

In this manner, in the nonvolatile semiconductor storage device, thememory cell array 52 is required to use a potential which is differentfrom the power supply potential. Therefore, it is desirable that atleast the memory cell array 52 and the peripheral circuit 54 beelectrically insulated and isolated from each other.

Therefore, with the use of the present invention, a semiconductor layercan be isolated into a plurality of element regions without beingdivided into island shapes. Steps resulting from the edge portion of thesemiconductor layer are not generated, and thus an insulating layer isformed over a flat semiconductor layer, leading to improvement incoverage of the semiconductor layer with the insulating layer.Therefore, a semiconductor device that is a highly reliable nonvolatilesemiconductor storage device in which defects such as a short andleakage current between a charge accumulation layer, a control gateelectrode layer, and a semiconductor layer that are caused by a coveragedefect of the semiconductor layer with an insulating layer can beprevented and a manufacturing method of such a semiconductor device canbe provided. Accordingly, further miniaturization and higher integrationof the semiconductor device are possible, and higher performance of thesemiconductor device can be achieved. In addition, because defects suchas shape defects of the film can be reduced, in the manufacturingprocess, the semiconductor device can be manufactured with good yield.

Embodiment Mode 3

In this embodiment mode, an example of a highly reliable semiconductordevice having a memory element (also referred to as a storage element)in which defects such as a short and leakage current between a gateelectrode layer and a semiconductor layer that are caused by a coveragedefect of a semiconductor layer with an insulating layer in asemiconductor element are prevented, will be described with reference todrawings. FIG. 15 is a top view of a semiconductor device of thisembodiment mode, FIG. 16A is a cross-sectional view taken along a lineI-I in FIG. 15, and FIG. 16B is a cross-sectional view taken along aline K-L in FIG. 15.

FIG. 15 shows an equivalent circuit of a NOR-type memory cell array inwhich a nonvolatile memory element M (M01, M02, or M03) is connected toa bit line BL (BL0, BL1, or BL2). In this memory cell array, word linesWL (WL1, WL2, and WL3) and bit lines BL (BL0, BL1, and BL2) are providedto intersect each other, and at each intersection, one of thenonvolatile memory elements M (M01, M02, or M03) is disposed. In aNOR-type memory cell array, a chain of each nonvolatile memory element M(M01, M02, or M03) is connected to one of the bit lines BL (BL0, BL1, orBL2). Sources of the nonvolatile memory elements are commonly connectedto source lines SL (SL0, SL1, and SL2).

In FIG. 15 and FIGS. 16A and 16B, drains of the memory elements M01,M02, and M03 are connected to the bit line BL 305 (305 a and 305 b), andsources thereof are connected to the source line SL 306. The memoryelement M01 includes an element region 302 a, a charge accumulationlayer 303 a, and a control gate electrode layer 304 a. The memoryelement M02 includes an element region 302 b, a charge accumulationlayer 303 b, and a control gate electrode layer 304 b. A firstinsulating layer 312, a second insulating layer 313, and an interlayerinsulating layer 314 are formed contiguous with the memory elements M01and M02. The element region 302 a and the element region 302 b each havea channel formation region and a high-concentration n-type impurityregion and a low-concentration impurity region serving as a source and adrain.

In the semiconductor layer, the element region 302 a included in thememory element M01 and the element region 302 b included in the memoryelement M02 are electrically isolated from each other by an elementisolation region 301 (301 a, 301 b, 301 c, 301 d, and 301 e).

The element isolation region is formed by selective addition of a firstimpurity element that does not contribute to conductivity and a secondimpurity element that imparts an opposite conductivity type to that of asource region and a drain region in the element region in order toelectrically isolate elements from each other in one semiconductorlayer.

As the first impurity element that does not contribute to conductivity,an impurity element of at least one or more kinds of oxygen, nitrogen,and carbon can be used. The element isolation region to which the firstimpurity element is added, conductivity is lowered by mixture of thefirst impurity element that does not contribute to conductivity, andresistance of the element isolation region is increased because itscrystallinity is lowered by a physical impact (it can also be referredto as a so-called sputtering effect) on the semiconductor layer atadding. In the element isolation region with the increased resistance,electron field-effect mobility is also lowered, and accordingly,elements can be electrically isolated from each other. On the otherhand, in a region to which an impurity element is not added, electronfield-effect mobility that is high enough to be able to serve as anelement is kept, and accordingly, the region can be used as an elementregion.

The element region has a source region, a drain region, and a channelformation region. The source region and the drain region are impurityregions having one conductivity type (for example, n-type impurityregions or p-type impurity regions). An impurity element that imparts anopposite conductivity type to that of the source region and the drainregion in the element region is added to the element isolation region,whereby the element isolation region is made to be an impurity regionhaving an opposite conductivity type to that of the source region andthe drain region in the element region that is adjacent to the elementisolation region. That is, in a case where the source region and thedrain region in the element region are n-type impurity regions, theadjacent element isolation region may be formed as a p-type impurityregion. Similarly, in a case where the source region and the drainregion in the element region are p-type impurity regions, the adjacentelement isolation region may be formed as an n-type impurity region. Theelement region and the element isolation region that are adjacent toeach other form a PN junction. Accordingly, the element regions can befurther insulated and isolated from each other by the element isolationregion provided between the element regions.

One feature of the present invention is that one semiconductor layer isisolated into a plurality of element regions in the manner thatresistance of the element isolation region by which the element regionsare insulated and isolated from each other is increased by addition ofthe first impurity element that does not contribute to conductivity, andfurther, a PN junction is formed in a position where the element regionand the element isolation region are in contact with each other byaddition of the second impurity element that imparts an oppositeconductivity type to that of the source region and the drain region inthe element region. By the present invention, the element regions can beisolated from each other by an effect caused by each of the firstimpurity element and the second impurity element. Thus, a higher effectof insulation and isolation of the element can be obtained.

FIG. 15 and FIGS. 16A and 16B show a case where a plurality of memoryelements is formed. Because the element isolation region 301 (301 a, 301b, 301 c, 301 d, and 301 e) is provided to be in contact with theelement regions 302 a and 302 b having the n-type impurity regions, theelement isolation region 301 may be formed as a p-type impurity regionby addition of an impurity element that imparts p-type conductivity (forexample, boron (B), aluminum (Al), gallium (Ga), or the like) as asecond impurity element that imparts an opposite conductivity type tothat of the source region and the drain region in the element region. Asa result, the n-type impurity region and the p-type impurity region arealternately adjacent to each other, whereby impurity regions having thesame conductivity can be insulated and isolated from each other.

The addition (introduction) of the first impurity element and the secondimpurity element in forming the element isolation region can beperformed by an ion implantation method, an (ion) doping method, or thelike.

The resistivity of the element isolation region is preferably greaterthan or equal to 1×10¹⁰ Ω·cm, and the concentration of the firstimpurity element such as oxygen, nitrogen, or carbon is preferablygreater than or equal to 1×10²⁰ Ω·cm⁻³ and less than 4×10²² Ω·cm⁻¹.

Crystallinity of the element isolation region is lowered by addition ofthe impurity element; therefore, it can be said that the elementisolation region is made to be amorphous. On the other hand, because theelement region is a crystalline semiconductor layer, in a case where asemiconductor element is formed in the element region, crystallinity ofthe channel formation region is higher than that of the elementisolation region, and high electron field-effect mobility can beobtained as a semiconductor element.

As the impurity element added to the element isolation region, a raregas element such as argon (Ar), neon (Ne), krypton (Kr), or xenon (Xe)may be used. By further addition of such a rare gas element that is anelement having comparatively high mass as well as oxygen, nitrogen, andcarbon, a physical impact on the semiconductor layer can be increased,whereby crystallinity of the element isolation region can be loweredmore effectively.

In FIG. 16B, the charge accumulation layer 303 b is formed to extendover the element region 302 b and the element isolation regions 301 dand 301 e in the semiconductor layer, with the first insulating layer312 interposed between the charge accumulation layer 303 b and thesemiconductor layer. In the present invention, the element isolationregion and the element region are provided in the continuoussemiconductor layer; therefore, the element isolation regions 301 d and301 e and the element region 302 b are contiguous. Thus, the surfacethereof has high flatness and no steep step.

The first insulating layer 312 is formed over the highly flatsemiconductor layer; therefore, coverage is good and shape defects arenot easily generated. Accordingly, defects such as leakage current and ashort can be prevented between the charge accumulation layers 303 a and303 b formed over the first insulating layer 312 and the element region302 a and 302 b, respectively. Thus, a semiconductor device that is anonvolatile semiconductor storage device of this embodiment mode can bea highly reliable semiconductor device in which defects such as a shortand leakage current between the charge accumulation layer and thesemiconductor layer that are caused by a coverage defect of thesemiconductor layer with the first insulating layer are prevented.

This embodiment mode can be implemented by being combined with otherembodiment modes shown in this specification.

Therefore, with the use of the present invention, a semiconductor layercan be isolated into a plurality of element regions without beingdivided into island shapes. Steps resulting from the edge portion of thesemiconductor layer are not generated, and thus an insulating layer isformed over a flat semiconductor layer, leading to improvement incoverage of the semiconductor layer with the insulating layer.Therefore, a semiconductor device that is a highly reliable nonvolatilesemiconductor storage device in which defects such as a short andleakage current between a charge accumulation layer, a control gateelectrode layer, a gate electrode layer, and a semiconductor layer thatare caused by a coverage defect of the semiconductor layer with aninsulating layer are prevented and a manufacturing method of such asemiconductor device can be provided. Accordingly, furtherminiaturization and higher integration of the semiconductor device arepossible, and higher performance of the semiconductor device can beachieved. In addition, because defects such as shape defects of the filmcan be reduced, in the manufacturing process, the semiconductor devicecan be manufactured with good yield.

Embodiment Mode 4

In this embodiment mode, an example of a highly reliable semiconductordevice having a memory element (also referred to as a storage element)in which defects such as a short and leakage current between a gateelectrode layer and a semiconductor layer that are caused by a coveragedefect of a semiconductor layer with an insulating layer in asemiconductor element are prevented, will be described with reference todrawings. FIG. 17 is a top view of a semiconductor device of thisembodiment mode, FIG. 18A is a cross-sectional view taken along a lineM-N in FIG. 17, and FIG. 18B is a cross-sectional view taken along aline O-P in FIG. 17.

In this embodiment mode, a case where a plurality of nonvolatile memoryelements is provided in one element region in the structure shown inEmbodiment Mode 2 will be described with reference to drawings. It is tobe noted that the explanation will be omitted in cases where one thesame as that in the above embodiment mode is referred to.

The semiconductor device shown in this embodiment mode is provided withelement regions 322 a and 322 b in a semiconductor layer, which areelectrically connected to bit lines BL0 and BL1, respectively, and eachof the element regions 322 a and 322 b is provided with a plurality ofnonvolatile memory elements (see FIG. 17 and FIGS. 18A and 18B).Specifically, in the element region 322 a, a NAND-type cell 350 a havinga plurality of nonvolatile memory elements M0 to M30 and M31 is providedbetween selection transistors S1 and S2. Also, in the element region 322b, a NAND-type cell 350 b having a plurality of nonvolatile memoryelements is provided between selection transistors. By an elementisolation region 321 being provided between the element regions 322 aand 322 b, the NAND-type cell 350 a and the NAND-type cell 350 b thatare close to each other can be insulated and isolated from each other.

Further, by a plurality of nonvolatile memory elements being provided inone element region, a nonvolatile memory element can be furtherintegrated, and thus a nonvolatile semiconductor storage device withlarge capacitance can be formed.

In FIG. 17 and FIGS. 18A and 18B, the selection transistors S1 and S2and the memory elements M0, M30, and M31 are provided over a substrate330 provided with an insulating layer 331. Gate electrode layers (SG2and SG1) 327 a and 327 b, charge accumulation layers 323 a, 323 b, and323 c, control gate electrode layers (WL31, WL30, and WL0) 324 a, 324 b,and 324 c, a first insulating layer 332, a second insulating layer 333,and an interlayer insulating layer 334 are provided. The selectiontransistor S1 is connected to the bit line BL0, and the selectiontransistor S2 is connected to a source line (SL0) 326.

In the semiconductor layer, the element region 322 a included in theNAND-type cell 350 a and the element region 322 b included in theNAND-type cell 350 b are electrically isolated from each other by theelement isolation region 321 (321 a, 321 b, 321 c, and 321 d).

The element isolation region is formed by selective addition of a firstimpurity element that does not contribute to conductivity and a secondimpurity element that imparts an opposite conductivity type to that of asource region and a drain region in the element region in order toelectrically isolate elements from each other in one semiconductorlayer.

As the first impurity element that does not contribute to conductivity,an impurity element of at least one or more kinds of oxygen, nitrogen,and carbon can be used. The element isolation region to which the firstimpurity element is added, conductivity is lowered by mixture of thefirst impurity element that does not contribute to conductivity, andresistance of the element isolation region is increased because itscrystallinity is lowered by a physical impact (it can also be referredto as a so-called sputtering effect) on the semiconductor layer atadding. In the element isolation region with the increased resistance,electron field-effect mobility is also lowered, and accordingly,elements can be electrically isolated from each other. On the otherhand, in a region to which an impurity element is not added, electronfield-effect mobility that is high enough to be able to serve as anelement is kept, and accordingly, the region can be used as an elementregion.

The element region has a source region, a drain region, and a channelformation region. The source region and the drain region are impurityregions having one conductivity type (for example, n-type impurityregions or p-type impurity regions). An impurity element that imparts anopposite conductivity type to that of the source region and the drainregion in the element region is added to the element isolation region,whereby the element isolation region is made to be an impurity regionhaving an opposite conductivity type to that of the source region andthe drain region in the element region that is adjacent to the elementisolation region. That is, in a case where the source region and thedrain region in the element region are n-type impurity regions, theadjacent element isolation region may be formed as a p-type impurityregion. Similarly, in a case where the source region and the drainregion in the element region are p-type impurity regions, the adjacentelement isolation region may be formed as an n-type impurity region. Theelement region and the element isolation region that are adjacent toeach other form a PN junction. Accordingly, the element regions can befurther insulated and isolated from each other by the element isolationregion provided between the element regions.

One feature of the present invention is that one semiconductor layer isisolated into a plurality of element regions in the manner thatresistance of the element isolation region by which the element regionsare insulated and isolated from each other is increased by addition ofthe first impurity element that does not contribute to conductivity, andfurther, a PN junction is formed in a position where the element regionand the element isolation region are in contact with each other byaddition of the second impurity element that imparts an oppositeconductivity type to that of the source region and the drain region inthe element region. By the present invention, the element regions can beisolated from each other by an effect caused by each of the firstimpurity element and the second impurity element. Thus, a higher effectof insulation and isolation of the element can be obtained.

FIG. 17 and FIGS. 18A and 18B show a case where a plurality of memoryelements is formed. Because the element isolation region 321 (321 a, 321b, 321 c, and 321 d) is provided to be in contact with the elementregions 322 a and 322 b having the n-type impurity regions, the elementisolation region 321 may be formed as a p-type impurity region byaddition of an impurity element that imparts p-type (for example, boron(B), aluminum (Al), gallium (Ga), or the like) as a second impurityelement that imparts an opposite conductivity type to that of the sourceregion and the drain region in the element region. As a result, then-type impurity region and the p-type impurity region are alternatelyadjacent to each other, whereby impurity regions having the sameconductivity can be insulated and isolated from each other.

The addition (introduction) of the first impurity element and the secondimpurity element in forming the element isolation region can beperformed by an ion implantation method, an (ion) doping method, or thelike.

The resistivity of the element isolation region is preferably greaterthan or equal to 1×10¹⁰ Ω·cm, and the concentration of the impurityelement such as oxygen, nitrogen, or carbon is preferably greater thanor equal to 1×10²⁰ Ω·cm⁻³ and less than 4×10²² Ω·cm⁻³.

Crystallinity of the element isolation region is lowered by addition ofthe impurity element; therefore, it can be said that the elementisolation region is made to be amorphous. On the other hand, because theelement region is a crystalline semiconductor layer, in a case where asemiconductor element is formed in the element region, crystallinity ofthe channel formation region is higher than that of the elementisolation region, and high electron field-effect mobility as asemiconductor element can be obtained.

As the impurity element added to the element isolation region, a raregas element such as argon (Ar), neon (Ne), krypton (Kr), or xenon (Xe)may be used. By further addition of such a rare gas element that is anelement having comparatively high mass as well as oxygen, nitrogen, andcarbon, a physical impact on the semiconductor layer can be increased,whereby crystallinity of the element isolation region can be loweredmore effectively.

In FIG. 18B, the charge accumulation layer 323 c is formed to extendover the element region 322 a and the element isolation regions 321 cand 321 d in the semiconductor layer, with the first insulating layer332 interposed between the charge accumulation layer 323 c and thesemiconductor layer. In the present invention, the element isolationregion and the element region are provided in the continuoussemiconductor layer; therefore, the element isolation regions 321 c and321 d and the element region 322 a are contiguous. Thus, the surfacethereof has high flatness and no steep step.

The first insulating layer 332 is formed over the highly flatsemiconductor layer; therefore, coverage is good and shape defects arenot easily generated. Accordingly, defects such as leakage current and ashort can be prevented between the charge accumulation layers 323 a, 323b, and 323 c formed over the first insulating layer 332 and the elementregion 322 a, respectively. Thus, a semiconductor device that is anonvolatile semiconductor storage device of this embodiment mode can bea highly reliable semiconductor device in which defects such as a shortand leakage current between the charge accumulation layer and thesemiconductor layer that are caused by a coverage defect of thesemiconductor layer with the first insulating layer are prevented.

This embodiment mode can be implemented by being combined with otherembodiment modes shown in this specification.

Therefore, with the use of the present invention, a semiconductor layercan be isolated into a plurality of element regions without beingdivided into island shapes. Steps resulting from the edge portion of thesemiconductor layer are not generated, and thus an insulating layer isformed over a flat semiconductor layer, leading to improvement incoverage of the semiconductor layer with the insulating layer.Therefore, a semiconductor device that is a highly reliable nonvolatilesemiconductor storage device in which defects such as a short andleakage current between a charge accumulation layer, a control gateelectrode layer, a gate electrode layer, and a semiconductor layer thatare caused by a coverage defect of the semiconductor layer with aninsulating layer are prevented and a manufacturing method of such asemiconductor device can be provided. Accordingly, furtherminiaturization and higher integration of the semiconductor device arepossible, and higher performance of the semiconductor device can beachieved. In addition, because defects such as shape defects of the filmcan be reduced, in the manufacturing process, the semiconductor devicecan be manufactured with good yield.

Embodiment Mode 5

In this embodiment mode, as a semiconductor device to which the presentinvention is applied, an example of a nonvolatile semiconductor storagedevice will be described. In the present invention, a plurality ofsemiconductor elements is manufactured in one semiconductor layerwithout division of the semiconductor layer into island shapes. Thepresent invention may be applied to all semiconductor elements to beprovided in a semiconductor device or part thereof. The presentinvention may be applied in accordance with a function required for asemiconductor element. An example of a semiconductor device to which thepresent invention is applied will be described with reference to FIGS.20A to 20D.

FIGS. 20A to 20D are each top views of a semiconductor device of thepresent invention, which are simply illustrated using a substrate, and aperipheral circuit portion and a memory element portion that areprovided over the substrate. In the semiconductor device of thisembodiment mode shown in FIGS. 20A to 20D, the memory element portionand the peripheral circuit portion are formed over the same substrate.FIG. 20A shows an example in which a peripheral circuit portion 472 anda memory element portion 471 are provided over a substrate 470, and asemiconductor layer is formed over an entire surface of the substrate470. Over the substrate 470, regions of the semiconductor layer that arein the peripheral circuit portion 472 and the memory element portion 471are isolated into an element isolation region, to which the presentinvention is applied, formed by addition of a first impurity elementthat does not contribute to conductivity and a second impurity elementthat imparts an opposite conductivity type to that of the elementregion, and an element region. Thereby, a plurality of semiconductorelements are faulted. The regions of the semiconductor layer other thanthose in the peripheral circuit portion 472 and the memory elementportion 471 provided over the substrate 470 may be made highly resistantin a similar manner to how the element isolation region in theperipheral circuit portion 472 and the memory element portion 471 is, byaddition of the first impurity element and the second impurity elementthat imparts an opposite conductivity type to that of the elementregion.

FIG. 20B shows an example in which a semiconductor layer is not formedover an entire surface of a substrate 475. A semiconductor layer in aregion other than a peripheral circuit portion 477 and a memory elementportion 476 provided over the substrate 475 is removed by etching or thelike. The peripheral circuit portion 477 and the memory element portion476 in FIG. 20B each have a structure in which a plurality ofsemiconductor elements is formed in one semiconductor layer by anelement isolation region that is a high-resistance region to which thefirst impurity element and the second impurity element that imparts anopposite conductivity type to that of the element region are added, in asimilar manner to the peripheral circuit portion 472 and the memoryelement portion 471 in FIG. 20A. The semiconductor layer in the regionover the substrate where semiconductor elements are not formed, may bemade highly resistant or removed, as shown in FIG. 20B. The region wherea plurality of semiconductor elements is positioned close to each other,for which a detailed isolation processing of a semiconductor layer isrequired, may have a structure in which a semiconductor layer is removedin a region where spacing between elements is comparatively wide or anelement is not formed by application of an element isolation method ofthe present invention.

FIG. 20C shows an example in which a different element isolation methodis applied in a semiconductor element provided over a substrate 480 inaccordance with a function and a size required. In FIG. 20C, aperipheral circuit portion 482 provided over the substrate 480 includesa semiconductor element that is processed into an island shape, andsemiconductor elements are isolated from each other by removal of asemiconductor layer by etching. Meanwhile, in a memory element portion481, an element isolation region to which a first impurity element and asecond impurity element that imparts an opposite conductivity type tothat of an element region are added is formed in one semiconductorlayer, and semiconductor elements are isolated from each other by theelement isolation region with the increased resistance. In a case wherea characteristic of a semiconductor element required is different in theperipheral circuit portion and the memory element portion, for example,a case where a voltage (for example, a (writing) voltage ofapproximately 10 to 20 V) applied to a semiconductor element in thememory element portion is higher than a voltage (for example, a voltageof approximately 3 to 5 V) applied to a semiconductor element in theperipheral circuit portion, it is more likely that a coverage defect ofthe semiconductor layer with a gate insulating layer results in anadverse effect. Accordingly, a semiconductor element may be used, inwhich an element region in one semiconductor layer is used for thememory element portion 481 in FIG. 20C, and an element region isolatedinto an island-shaped semiconductor layer is used for the peripheralcircuit portion 482. Even in a case where a memory element portion inwhich a voltage of from approximately 10 to 20 V is required to writeand erase, and a peripheral circuit portion that operates at a voltageof from approximately 3 to 7 V to mainly input and output data andcontrol commands are formed over one substrate, mutual interference dueto the difference in the voltages applied to each element can beprevented.

Similarly to FIG. 20C, FIG. 20D shows an example in which a differentelement isolation method is applied in accordance with a function and asize required in a semiconductor element provided over a substrate 485.In. FIG. 20D, a peripheral circuit portion 487 b provided over thesubstrate 485 includes a semiconductor element that is processed into anisland shape, and semiconductor elements are isolated from each other byremoval of a semiconductor layer by etching. Meanwhile, in a peripheralcircuit portion 487 a and a memory element portion 486, an elementisolation region to which a first impurity element and a second impurityelement that imparts an opposite conductivity type to that of an elementregion are added is formed in one semiconductor layer, and semiconductorelements are isolated from each other by the element isolation region.In this manner, a structure in which elements are selectively isolatedfrom each other by an island-shaped semiconductor layer in theperipheral circuit portion 487 b and a structure in which elements areisolated from each other by an element isolation region in onesemiconductor layer in the peripheral circuit portion 487 b and thememory element portion 486 may be used in combination appropriately inaccordance with a circuit configuration provided over a substrate.

Different characteristics are required for each semiconductor elementprovided over a substrate in accordance with functions, and a shape of asemiconductor element (for example, a thickness of a gate insulatinglayer) is changed in accordance with the characteristic required. In aregion with a detailed structure in which semiconductor elements areclose to each other, a structure is employed in which an elementisolation region is provided in one semiconductor layer and a pluralityof semiconductor elements are formed. Meanwhile, in a region wherespacing between elements is comparatively wide or thinning of a gateinsulating layer is not required so much from a structural point ofview, a semiconductor layer is removed and a plurality of semiconductorelements can be manufactured as island-shaped semiconductor layers. Byappropriate selection of different element separation methods inaccordance with characteristics required over a substrate, asemiconductor device with high performance which is capable of highspeed response and is highly reliable can be manufactured.

The element isolation region is formed by selective addition of a firstimpurity element that does not contribute to conductivity and a secondimpurity element that imparts an opposite conductivity type to that of asource region and a drain region in the element region in order toelectrically isolate elements from each other in one semiconductorlayer.

As the first impurity element that does not contribute to conductivity,an impurity element of at least one or more kinds of oxygen, nitrogen,and carbon can be used. The element isolation region to which the firstimpurity element is added, conductivity is lowered by mixture of thefirst impurity element that does not contribute to conductivity, andresistance of the element isolation region is increased because itscrystallinity is lowered by a physical impact (it can also be referredto as a so-called sputtering effect) on the semiconductor layer atadding. In the element isolation region with the increased resistance,electron field-effect mobility is also lowered, and accordingly,elements can be electrically isolated from each other. On the otherhand, in a region to which an impurity element is not added, electronfield-effect mobility that is high enough to be able to serve as anelement is kept, and accordingly, the region can be used as an elementregion.

The element region has a source region, a drain region, and a channelformation region. The source region and the drain region are impurityregions having one conductivity type (for example, n-type impurityregions or p-type impurity regions). An impurity element that imparts anopposite conductivity type to that of the source region and the drainregion in the element region is added to the element isolation region,whereby the element isolation region is made to be an impurity regionhaving an opposite conductivity type to that of the source region andthe drain region in the element region that is adjacent to the elementisolation region. That is, in a case where the source region and thedrain region in the element region are n-type impurity regions, theadjacent element isolation region may be formed as a p-type impurityregion. Similarly, in a case where the source region and the drainregion in the element region are p-type impurity regions, the adjacentelement isolation region may be formed as an n-type impurity region. Theelement region and the element isolation region that are adjacent toeach other form a PN junction. Accordingly, the element regions can befurther insulated and isolated from each other by the element isolationregion provided between the element regions.

One feature of the present invention is that one semiconductor layer isisolated into a plurality of element regions in the manner thatresistance of the element isolation region by which the element regionsare insulated and isolated from each other is increased by addition ofthe first impurity element that does not contribute to conductivity, andfurther, PN junctions are successively (repeadedly) formed in positionswhere the element region and the element isolation region are in contactwith each other by addition of the second impurity element that impartsan opposite conductivity type to that of the source region and the drainregion in the element region. By the present invention, the elementregions can be isolated from each other by an effect caused by each ofthe first impurity element and the second impurity element. Thus, ahigher effect of insulation and isolation of the element can beobtained.

The resistivity of the element isolation region is preferably greaterthan or equal to 1×10¹⁰ Ω·cm, and the concentration of the firstimpurity element such as oxygen, nitrogen, or carbon is preferablygreater than or equal to 1×10²⁰ Ω·cm⁻³ and less than 4×10²² Ω·cm⁻³.

Crystallinity of the element isolation region is lowered by addition ofthe impurity element; therefore, it can be said that the elementisolation region is made to be amorphous. On the other hand, because theelement region is a crystalline semiconductor layer, in a case where asemiconductor element is formed in the element region, crystallinity ofthe channel formation region is higher than that of the elementisolation region, and high electron field-effect mobility can beobtained as a semiconductor element.

As the impurity element added to the element isolation region, a raregas element such as argon (Ar), neon (Ne), krypton (Kr), or xenon (Xe)may be used. By further addition of such a rare gas element that is anelement having comparatively high mass as well as oxygen, nitrogen, andcarbon, a physical impact on the semiconductor layer can be increased,whereby crystallinity of the element isolation region can be loweredmore effectively.

Therefore, according to this embodiment mode, a semiconductor devicethat is a highly reliable nonvolatile semiconductor memory device inwhich defects such as a short and leakage current between a chargeaccumulation layer, a control gate electrode layer, a gate electrodelayer, and a semiconductor layer that are caused by a coverage defect ofthe semiconductor layer with an insulating layer are prevented and amanufacturing method of such a semiconductor device can be provided.Accordingly, further miniaturization and higher integration of thesemiconductor device are possible, and higher performance of thesemiconductor device can be achieved. In addition, because defects suchas shape defects of the film can be reduced, in the manufacturingprocess, the semiconductor device can be manufactured with good yield.

Embodiment Mode 6

In this embodiment mode, an example of a highly reliable semiconductordevice having a memory element (also referred to as a storage element)in which defects such as a short and leakage current between a gateelectrode layer and a semiconductor layer that are caused by a coveragedefect of a semiconductor layer with an insulating layer in asemiconductor element are prevented, will be described with reference todrawings. FIG. 11A is a top view of a semiconductor device of thisembodiment mode, and FIG. 11B is a cross-sectional view taken along aline X-Y in FIG. 11A.

As shown in FIG. 11A, a memory element portion 404, a circuit portion421, and an antenna 431 that are included in a semiconductor devicehaving a memory element are formed over a substrate 400. A state shownin FIGS. 11A and 11B is in the middle of a manufacturing process, inwhich the memory element portion, the circuit portion, and the antennahave been formed over the substrate 400 capable of resisting themanufacturing condition. The material and manufacturing process can beselected similarly to Embodiment Mode 3 for manufacturing.

Over the substrate 400, a memory element 441 is provided in the memoryelement portion 404 while a transistor 442 is provided in the circuitportion 421, with a peeling layer 452 and an insulating layer 453interposed therebetween. An insulating layer 455 is formed over thememory element 441 and the transistor 442.

In the semiconductor device shown in FIG. 11B, an antenna 431 a, anantenna 431 b, an antenna 431 c, and an antenna 431 d are formed overthe insulating layer 455. The antenna 431 c is formed to be in contactwith a wiring layer 456 b in an opening which is formed in theinsulating layer 455 so as to reach the wiring layer 456 b, whichelectrically connect the antenna to the memory element portion 404 andthe circuit portion 421.

This embodiment mode can be freely combined with the above embodimentmode. The semiconductor device manufactured in this embodiment mode canbe provided over a flexible substrate by being peeled from a substratethrough a peeling step and by being adhered to a flexible substrate.Thus, a flexible semiconductor device can be obtained.

A flexible semiconductor device formed by attachment of a semiconductordevice to a flexible substrate is also referred to as an IC film. The ICfilm is a flexible semiconductor device having a thickness of less thanor equal to 100 μm, preferably, less than or equal to 50 μm, and morepreferably, less than or equal to 20 μm, in which a thickness of anincluded semiconductor layer of less than or equal to 100 μm,preferably, less than or equal to 70 μm.

A flexible substrate corresponds to a film obtained by stacking anadhesive synthetic resin film (e.g., acrylic synthetic resin orepoxy-based synthetic resin) and any of a substrate made of PET(polyethylene terephthalate), PEN (polyethylene naphthalate), PES(polyethersulfone), polypropylene, polypropylene sulfide, polycarbonate,polyetherimide, polyphenylene sulfide, polyphenylene oxide, polysulfone,polyphthalamide, or the like; a film made of polypropylene, polyester,vinyl, polyvinyl fluoride, vinyl chloride, or the like; paper made of afibrous material; and a base film (e.g., polyester, polyamide, inorganicdeposited film, or paper). A film is obtained by applying thermaltreatment and pressure treatment to a treatment subject. When conductingthermal treatment and pressure treatment, an adhesive layer provided onthe outermost surface of the film or a layer (which is not an adhesivelayer) provided on the outermost surface is melted by thermal treatmentand then attached to a base substrate by applying pressure. The basesubstrate may be either provided with or not provided with an adhesivelayer. An adhesive layer corresponds to a layer containing an adhesivesuch as a thermal curing resin, a UV curing resin, an epoxy resin, or aresin additive.

The semiconductor device having memory elements of the present inventionmay be manufactured by the steps of forming memory elements over a firstsubstrate which can withstand the process conditions (e.g., temperature)and then transferring the memory elements to a second substrate. Inaddition, in this specification, “to transfer” means “to peel memoryelements formed over a first substrate off the first substrate and movethem to a second substrate.” That is, it can also be said that “to movethe position of providing memory elements to another substrate.”

It is to be noted that, for the step of transferring memory elements toanother substrate, it is possible to appropriately use any of thefollowing methods: a method in which a peeling layer and an insulatinglayer are formed between a substrate and an element formation layer, ametal oxide film is provided between the peeling layer and theinsulating layer, and the metal oxide film is weakened bycrystallization so that the element formation layer is peeled off thesubstrate; a method in which an amorphous silicon film containinghydrogen is provided between a highly heat-resistant substrate and anelement formation layer, and the amorphous silicon film is removed bylaser irradiation or etching so that the element formation layer ispeeled off the substrate; or a method in which a peeling layer and aninsulating layer are formed between a substrate and an element formationlayer, a metal oxide film is provided between the peeling layer and theinsulating layer, the metal oxide film is weakened by crystallization,and a part of the peeling layer is removed by etching using a solutionor a halogen fluoride gas such as NF₃, BrF₃, or ClF₃ so that separationoccurs at the weakened metal oxide film; or a method in which asubstrate over which an element formation layer is formed is removedmechanically or by etching with a solution or a halogen fluoride gassuch as NF₃, BrF₃, or ClF₃. Alternatively, it is also possible to use amethod in which a film containing nitrogen, oxygen, hydrogen, or thelike (e.g., an amorphous silicon film containing hydrogen, an alloy filmcontaining hydrogen, or an alloy film containing oxygen) is used as apeeling layer, and the peeling layer is irradiated with laser light sothat nitrogen, oxygen, or hydrogen contained in the peeling layer isdissipated as a gas, thereby promoting separation between the elementformation layer and the substrate.

When the above-described peeling methods are combined, the transfer stepcan be conducted easily. That is, peeling can be conducted with physicalforce (e.g., by a machine or the like) after making it easier for thepeeling layer and the element formation layer to be peeled from eachother by conducting laser irradiation, etching the peeling layer with agas or a solution, and/or mechanically removing the peeling layer usinga keen knife.

The antenna may be provided to overlap with the memory element portionor provided around the memory element portion without overlapping. Inaddition, when the antenna is provided to overlap with the memoryelement portion, it may overlap with either a part of or an entiresurface of the memory element portion. When the antenna portion and thememory element portion overlap with each other, it is possible to reducenoise or the like which is superposed on signals that the antennacommunicates or reduce malfunctions of the semiconductor device due tothe effect of fluctuation of electromotive force which is generated byelectromagnetic induction. Thus, the reliability of the semiconductordevice is improved. Further, the size of the semiconductor device can bereduced.

The signal transmission method of the above-described semiconductordevice which is capable of wireless data communication can be anelectromagnetic coupling method, an electromagnetic induction method, amicrowave method, or the like. The transmission method can be selectedappropriately by a practitioner in consideration of the intendedpurpose, and an optimal antenna may be provided in accordance with thetransmission method.

For example, in the case of using an electromagnetic coupling method oran electromagnetic induction method (e.g., 13.56 MHz) as the signaltransmission method of the semiconductor device, a conductive layerserving as an antenna is formed in an annular form (e.g., a loopantenna) or a helical form (e.g., a spiral antenna) in order to utilizeelectromagnetic induction which occurs with changes in magnetic density.

In the case of using a microwave method (e.g., UHF band (860 to 960 MHz)or 2.45 GHz band) as the signal transmission method of the semiconductordevice, the shape (e.g., length) of a conductive layer serving as anantenna may be appropriately set in consideration of the wavelength ofan electromagnetic wave used for signal transmission. For example, aconductive layer serving as an antenna may be formed in a linear form(e.g., a dipole antenna), a flat form (e.g., a patch antenna), a ribbonform, or the like. The shape of the conductive layer serving as theantenna is not limited to the linear form. For example, the conductivelayer may be provided in a curved form, a serpentine form, or the likein consideration of the wavelength of electromagnetic waves.

The conductive layer serving as the antenna is formed using a conductivematerial by a CVD method, a sputtering method, a printing method such asscreen printing or gravure printing, a droplet discharge method, adispensing method, a plating method, or the like. The conductivematerial is selected from an element such as aluminum (Al), titanium(Ti), silver (Ag), copper (Cu), gold (Au), platinum (Pt), nickel (Ni),palladium (Pd), tantalum (Ta), and molybdenum (Mo), or an alloy materialor a compound material containing such an element as a main component.In addition, the conductive layer may be formed to have either asingle-layer structure or a stacked structure.

For example, in the case of forming the conductive layer serving as theantenna by a screen printing method, it may be provided by selectivelyprinting a conductive paste in which conductive particles with aparticle size of several nm to several tens of μm are dissolved ordispersed in an organic resin. The conductive particles can be at leastone of metal particles selected from silver (Ag), gold (Ag), copper(Cu), nickel (Ni), platinum (Pt), palladium (Pd), tantalum (Ta),molybdenum (Mo), and titanium (Ti); fine particles of silver halide; ordispersive nanoparticles. In addition, the organic resin included in theconductive paste can be one or more of organic resins serving as abinder, a solvent, a dispersing agent, and a coating material for themetal particles. Typically, an organic resin such as an epoxy resin anda silicone resin can be given as examples. In addition, it is preferableto form a conductive layer by extruding a conductive paste and bakingit. For example, in the case of using fine particles (e.g., a particlesize of 1 to 100 nm) containing silver as the main component for amaterial of the conductive paste, a conductive layer can be obtained bybaking and hardening the conductive paste at temperatures in the rangeof 150 to 300° C. It is also possible to use fine particles of solder orlead-free solder. In that case, fine particles with a particle size of20 μm or less are preferably used. Solder and lead-free solder have theadvantages of low cost. Besides the above-described materials, ceramic,ferrite, or the like may also be used for the antenna.

In the case of using the electromagnetic coupling method or theelectromagnetic induction method, and forming the semiconductor devicehaving the antenna to be in contact with metal, it is preferable toprovide a magnetic material having magnetic permeability between thesemiconductor device and the metal. When the semiconductor device havingthe antenna is provided in contact with the metal, eddy current flowsthrough the metal in accordance with changes in magnetic field, and inturn, a demagnetizing field which is generated by the eddy currentweakens the changes in magnetic field, so that the communicationdistance decreases. Therefore, by providing a magnetic material havingmagnetic permeability between the semiconductor device and the metal,eddy current which flows through the metal can be suppressed, and thus adecrease in communication distance can be suppressed. As a magneticmaterial, ferrite or a thin metal film having high magnetic permeabilityand low loss of high frequency can be used.

In addition, when providing the antenna, it is possible to directly formsemiconductor elements such as transistors and a conductive layerserving as an antenna over one substrate. Alternatively, it is alsopossible to provide semiconductor elements and a conductive layerserving as an antenna over different substrates, and then attach thesubstrates to each other so that the semiconductor elements and theantenna are electrically connected.

The present invention is applied to the memory element 441 and thetransistor 442. The channel formation regions of these elements areformed in element regions which are provided in one semiconductor layer.The memory element and the transistors are isolated from each other bythe element isolation regions 457 a, 457 b, 457 c, 457 d, and 457 eformed by addition of first impurity elements and second impurityelements. In this manner, when the present invention is employed, asemiconductor layer can be isolated into a plurality of element regionswithout being divided into island shapes, and a plurality ofsemiconductor elements can be manufactured. Hence, steps resulting fromthe edge portion of the semiconductor layer are not generated, and thusan insulating layer is formed over a flat semiconductor layer, leadingto improvement in coverage of the semiconductor layer with theinsulating layer.

Thus, according to this embodiment mode, a highly reliable semiconductordevice a having memory element in which defects such as a short betweena charge accumulation layer, a control gate electrode layer, a gateelectrode layer, and a semiconductor layer and a leakage current thatare caused by a coverage defect of the semiconductor layer with aninsulating layer are prevented and a manufacturing method of such asemiconductor device can be provided. Accordingly, furtherminiaturization and higher integration of the semiconductor devicehaving a memory element are possible, and higher performance of thesemiconductor device can be achieved. In addition, because defects suchas a shape defect of the film can be reduced, in the manufacturingprocess, the semiconductor device can be manufactured with good yield.

Embodiment Mode 7

In this embodiment mode, an example of a highly reliable semiconductordevice having a CMOS circuit and a memory element in which defects suchas a short and leakage current between a gate electrode layer and asemiconductor layer that are caused by a coverage defect of asemiconductor layer with an insulating layer in a semiconductor elementare prevented, will be described with reference to drawings. Amanufacturing method of a semiconductor device in this embodiment modewill be described in detail with reference to FIGS. 5A to 5F and FIGS.6A to 6E.

It is to be noted that selection transistors provided in the memoryportion require a higher driving voltage than transistors provided inthe logic portion; therefore, it is preferable to vary, for example, thethickness of a gate insulating layer or the like of the transistorsprovided in the memory portion and the thickness of a gate insulatinglayer or the like of the transistors provided in the logic portion. Forexample, in order to obtain transistors with low driving voltage andsmall variations in threshold voltage, it is preferable to form thinfilm transistors having a thin gate insulating layer. On the other hand,in order to obtain transistors with high driving voltage and a gateinsulating layer with high dielectric strength, it is preferable to formthin film transistors having a thick gate insulating layer.

Accordingly, this embodiment mode will describe a case of forming a thininsulating layer for the transistors in the logic portion, which requirea low driving voltage and small variations in threshold voltage, andforming a thick insulating layer for the transistors in the memoryportion, which require a high driving voltage and high dielectricstrength of a gate insulating layer.

As base films over a substrate 100 having an insulating surface, aninsulating layer 112 a made of a silicon nitride oxide film with athickness of 10 to 200 nm (preferably, 50 to 150 nm), and an insulatinglayer 112 b made of a silicon oxynitride film with a thickness of 50 to200 nm (preferably, 100 to 150 nm) are stacked by a sputtering method, aPVD (Physical Vapor Deposition) method, or a CVD (Chemical VaporDeposition) method such as a low pressure CVD (LPCVD) method or a plasmaCVD method. Alternatively, it is also possible to use acrylic acid;methacrylic acid; derivatives thereof; thermally stable polymers such aspolyimide, aromatic polyamide, or polybenzimidazole; or a siloxaneresin. It is to be noted that the siloxane resin corresponds to a resinhaving a Si—O—Si bond. Siloxane has a skeletal structure with the bondof silicon (Si) and oxygen (O). As a substituent, an organic groupcontaining at least hydrogen (e.g., an alkyl group or an aryl group) isused. Alternatively, a fluoro group may be used as the substituent. As afurther alternative, both an organic group containing at least hydrogenand a fluoro group may be used as the substituent. Further, other resinmaterials can be used such as a vinyl resin (e.g., polyvinyl alcohol orpolyvinyl butyral), an epoxy rein, a phenol resin, a novolac resin, anacrylic rein, a melamine resin, or a urethane resin. In addition, it isalso possible to use an organic material such as benzocyclobutene,parylene, fluorinated arylene ether, or polyimide, or a compositionmaterial containing water-soluble homopolymers and water-solublecopolymers. Further, an oxazole resin such as photo-curingpolybenzoxazole can also be used.

Further, a droplet discharge method, a printing method (a method bywhich patterns are formed such as screen printing or offset printing), acoating method such as spin coating, a dipping method, a dispensingmethod, or the like can be used. In this embodiment mode, the insulatinglayer 112 a and the insulating layer 112 b are formed by a plasma CVDmethod. As the substrate 100, a glass substrate, a quartz substrate, ametal substrate, or a stainless steel substrate having an insulatinglayer formed on its surface can be used. Alternatively, a plasticsubstrate which can withstand the processing temperature in thisembodiment mode, or a flexible substrate such as a film can also beused. As a plastic substrate, a substrate made of PET (polyethyleneterephthalate), PEN (polyethylene naphthalate), PES (polyethersulfone),or the like can be used. As a flexible substrate, a synthetic resin suchas acrylic can be used.

As the insulating layers serving as base films, silicon oxide, siliconnitride, silicon oxynitride, silicon nitride oxide, or the like can beused, and either a single-layer structure or a stacked structure of twoor three layers can be employed.

Next, a semiconductor layer is formed over the base films. Thesemiconductor layer may be formed to a thickness of 25 to 200 nm(preferably, 30 to 150 nm) by various methods (e.g., a sputteringmethod, an LPCVD method, or a plasma CVD method). In this embodimentmode, it is preferable to use a crystalline semiconductor layer which isobtained by crystallizing an amorphous semiconductor layer by laserirradiation.

As a method for forming the crystalline semiconductor layer, variousmethods (e.g., a laser crystallization method, a thermal crystallizationmethod, or a them al crystallization method using an element whichpromotes the crystallization such as nickel) may be used. Further, whena microcrystalline semiconductor is crystallized by laser irradiation,the crystallinity thereof can be increased. When an element whichpromotes the crystallization is not used, heating is conducted under anitrogen atmosphere at 500° C. for one hour before conducting laserirradiation for an amorphous semiconductor layer, so that theconcentration of hydrogen contained in the amorphous semiconductor layeris reduced to 1×10²⁰ atoms/cm³ or less. This is because when anamorphous semiconductor layer containing much hydrogen is irradiatedwith laser light, the amorphous semiconductor layer will be destroyed.For the thermal treatment for crystallization, it is possible to use aheating oven, laser irradiation, irradiation with light emitted from alamp (also called lamp annealing), or the like. As a heating method,there is an RTA method such as GRTA (Gas Rapid Thermal Annealing) methodor an LRTA (Lamp Rapid Thermal Annealing) method. GRTA is a method ofthermal treatment using a high-temperature gas, and LRTA is a method ofthermal treatment using light emitted from a lamp.

Alternatively, in the crystallization step for forming a crystallinesemiconductor layer by crystallizing an amorphous semiconductor layer,the crystallization may be conducted by adding an element which promotesthe crystallization (also called a catalytic element or a metal element)to the amorphous semiconductor layer and applying thermal treatment (550to 750° C. for 3 minutes to 24 hours) thereto. The element whichpromotes the crystallization can be one or more of iron (Fe), nickel(Ni), cobalt (Co), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium(Os), iridium (Tr), platinum (Pt), copper (Cu), and gold (Au).

As a method for introducing a metal element into the amorphoussemiconductor layer, any method by which the metal element can remain onthe surface or inside of the amorphous semiconductor layer can be used.For example, a sputtering method, a CVD method, a plasma treatmentmethod (including a plasma CVD method), an adsorption method, or amethod of applying a metal-salt solution can be used. Above all, themethod using a solution is simple and advantageous in that theconcentration of the metal element can be easily controlled. Inaddition, in order to improve the wettability of the surface of theamorphous semiconductor layer and spread an aqueous solution over anentire surface of the amorphous semiconductor layer, it is desirable toform an oxide film by UV irradiation under an oxygen atmosphere, athermal oxidation method, treatment with ozone water containing hydroxylradical or with hydrogen peroxide, or the like.

In order to remove or reduce the element which promotes thecrystallization from the crystalline semiconductor layer, asemiconductor layer containing an impurity element is formed in contactwith the crystalline semiconductor layer so that it can serve as agettering sink. As the impurity element, an impurity element thatimparts n-type conductivity, an impurity element that imparts p-typeconductivity, a rare gas element, or the like can be used. For example,one or more elements selected from phosphorus (P), nitrogen (N), arsenic(As), antimony (Sb), bismuth (Bi), boron (B), helium (He), neon (Ne),argon (Ar), Kr (krypton), and Xe (xenon) can be used. A semiconductorlayer containing a rare gas element is formed over the crystallinesemiconductor layer containing the element which promotes thecrystallization, and thermal treatment (550 to 750° C. for 3 minutes to24 hours) is applied thereto. The element which promotes thecrystallization and is contained in the crystalline semiconductor layermoves toward the semiconductor layer containing the rare gas element sothat the element which promotes the crystallization and is contained inthe crystalline semiconductor layer is removed or reduced. After that,the semiconductor layer containing the rare gas element serving as thegettering sink is removed.

Laser irradiation can be conducted by scanning laser and thesemiconductor layer relative to each other. In addition, a marker may beformed in order to overlap beams with high accuracy or to control thelaser irradiation starting position and the laser irradiationtermination position in the laser irradiation. The marker may be formedon the substrate at the same time as the formation of the amorphoussemiconductor layer.

When laser irradiation is used, a continuous wave (CW) laser beam or apulsed laser beam can be used. As a laser beam herein, one or more ofthe following can be used: gas lasers such as an Ar laser, a Kr laser,and an excimer laser; a laser in which a medium such assingle-crystalline YAG, YVO₄, forsterite (Mg₂SiO₄), YAlO₃, or GdVO₄, orpolycrystalline (ceramic) YAG, Y₂O₃, YVO₄, YAlO₃, or GdVO₄ is doped withone or more of dopants such as Nd, Yb, Cr, Ti, Ho, Er, Tm, and Ta; aglass laser; a ruby laser; an alexandrite laser; a Ti:sapphire laser; acopper vapor laser; and a gold vapor laser. When irradiation isconducted with the fundamental wave of such a laser beam or the secondto fourth harmonics of the fundamental wave, crystals with a large grainsize can be obtained. For example, the second harmonic (532 nm) or thethird harmonic (355 nm) of an Nd:YVO₄ laser (the fundamental wave of1064 nm) can be used. This laser can be either a CW laser or a pulsedlayer. When the laser is used as a CW laser, a laser power density ofabout 0.01 to 100 MW/cm² (preferably, 0.1 to 10 MW/cm²) is required, andirradiation is conducted with a scanning rate set at about 10 to 2000cm/sec.

It is to be noted that although the laser in which a medium such assingle-crystalline YAG, YVO₄, forsterite (Mg₂SiO₄), YAlO₃, or GdVO₄, orpolycrystalline (ceramic) YAG, Y₂O₃, YVO₄, YAlO₃, or GdVO₄ is doped withone or more of dopants such as Nd, Yb, Cr, Ti, Ho, Er, Tm, and Ta; an Arion laser, or a Ti:sapphire laser can be used as a CW laser, it can alsobe used as a pulsed laser with a repetition rate of 10 MHz or more bybeing combined with a Q-switch operation or mode locking. When a laserbeam with a repetition rate of 10 MHz or more is used, it is possiblefor a semiconductor layer to be irradiated with the next pulse after itis melted by the previous laser but before it becomes solidified.Therefore, unlike the case of using a pulsed laser with a low repetitionrate, it is possible to move a solid-liquid interface continuously inthe semiconductor layer. Thus, crystal grains which have growncontinuously in the scanning direction can be obtained.

When ceramic (polycrystals) is used as a medium, the medium can beformed into a desired shape in a short time at low cost. When singlecrystals are used, a medium with a columnar shape having a diameter ofseveral mm and a length of several tens of mm is usually used. However,when ceramic is used, a medium larger than the case of using singlecrystals can be foamed.

In both cases of using single crystals and polycrystals, theconcentration of the dopant such as Nd or Yb contained in the mediumwhich directly contributes to light emission cannot be changed largely.Therefore, there is a limitation to improving the output of the laser byincreasing the concentration of the dopant. However, in the case ofusing ceramic, a drastic improvement in output can be achieved becausethe size of the medium can be significantly increased than the case ofusing single crystals.

Further, in the case of using ceramic, a medium with a parallelepipedshape or a rectangular parallelepiped shape can be formed easily. Whensuch a medium is used and oscillated light is made travel within themedium in a zigzag manner, the oscillation path can be made long.Therefore, large amplification can be achieved and high output can beobtained. In addition, since a laser beam emitted from the medium withsuch a shape has a quadrangular cross section, it can easily be shapedinto a linear beam unlike the case of using a circular beam, which isadvantageous. When the laser beam emitted in this manner is shaped withoptics, a linear beam with a short side of 1 mm or less and a long sideof several mm to several m can be obtained easily. In addition, when anexcitation light is uniformly shone on the medium, a linear beam withuniform energy distribution in the long-side direction can be obtained.Further, it is preferable that the laser be emitted on the semiconductorlayer at an incident angle of θ (0<θ<90°) in order to preventinterference of laser.

By irradiation of the semiconductor layer with such a linear beam, anentire surface of the semiconductor layer can be irradiated moreuniformly. In the case where uniform irradiation is required from oneend to the other end of the linear laser beam, it is necessary toexercise ingenuity, for example, by using slits or the like so as toshield light at a portion where energy is attenuated.

It is also possible to irradiate the semiconductor layer with laserlight in an inert gas atmosphere such as a rare gas or nitrogen.Accordingly, roughness of the surface of the semiconductor layer causedby laser irradiation can be suppressed, and variations in the thresholdvoltage of transistors caused by variations in interface state densitycan be suppressed.

Crystallization of the amorphous semiconductor layer may also beconducted by combining thermal treatment and laser irradiation.Alternatively, one of thermal treatment and laser irradiation may beconducted a plurality of times.

The thusly obtained semiconductor layer may be doped with a small amountof an impurity element (e.g., boron or phosphorus) in order to controlthe threshold voltage of thin film transistors. Alternatively, suchdoping with the impurity element may be conducted before thecrystallization step of the amorphous semiconductor layer. When theamorphous semiconductor layer is doped with an impurity element and thensubjected to thermal treatment to be crystallized, activation of theimpurity element can also be performed. In addition, defects caused indoping can be remedied.

An impurity element is selectively added to the semiconductor layer thatis a crystalline semiconductor layer to form an element isolationregion. The semiconductor layer is isolated into a plurality of elementregions by the element isolation region. Over the semiconductor layer,mask layers 103 a, 103 b, 103 c, and 103 d are formed, and an impurityelement 104 that does not contribute to conductivity is added. By theaddition of the impurity element 104 that does not contribute toconductivity, element isolation regions 651 a, 651 b, 651 c, 651 d, 651e, 651 f, 651 g, and 651 h and element regions 102 a, 102 b, 102 c, and102 d that are insulated and isolated from each other by those elementisolation region are formed in the semiconductor layer (see FIG. 5A).

The element isolation region is formed by selective addition of a firstimpurity element that does not contribute to conductivity and a secondimpurity element that imparts an opposite conductivity type to that of asource region and a drain region in the element region in order toelectrically isolate elements from each other in one semiconductorlayer.

As the first impurity element that does not contribute to conductivity,an impurity element of at least one or more kinds of oxygen, nitrogen,and carbon can be used. The element isolation region to which the firstimpurity element is added, conductivity is lowered by mixture of thefirst impurity element that does not contribute to conductivity, andresistance of the element isolation region is increased because itscrystallinity is lowered by a physical impact (it can also be referredto as a so-called sputtering effect) on the semiconductor layer atadding. In the element isolation region with the increased resistance,electron field-effect mobility is also lowered, and accordingly,elements can be electrically isolated from each other. On the otherhand, in a region to which an impurity element is not added, electronfield-effect mobility that is high enough to be able to serve as anelement is kept, and accordingly, the region can be used as an elementregion.

The element region has a source region, a drain region, and a channelformation region. The source region and the drain region are impurityregions having one conductivity type (for example, n-type impurityregions or p-type impurity regions). An impurity element that imparts anopposite conductivity type to that of the source region and the drainregion in the element region is added to the element isolation region,whereby the element isolation region is formed as an impurity regionhaving an opposite conductivity type to that of the source region andthe drain region in the adjacent element region. That is, in a casewhere the source region and the drain region in the element region aren-type impurity regions, the adjacent element isolation region may beformed as a p-type impurity region. Similarly, in a case where thesource region and the drain region in the element region are p-typeimpurity regions, the adjacent element isolation region may be formed asan n-type impurity region. The element region and the element isolationregion that are adjacent to each other form a PN junction. Accordingly,the element regions can be further insulated and isolated from eachother by the element isolation region provided between the elementregions.

One feature of the present invention is that one semiconductor layer isisolated into a plurality of element regions in the manner thatresistance of the element isolation region by which the element regionsare insulated and isolated from each other is increased by addition ofthe first impurity element that does not contribute to conductivity, andfurther, a PN junction is formed in a position where the element regionand the element isolation region are in contact with each other byaddition of the second impurity element that imparts an oppositeconductivity type to that of the source region and the drain region inthe element region. By the present invention, the element regions can beisolated from each other by an effect caused by each of the firstimpurity element and the second impurity element. Thus, a higher effectof insulation and isolation of the element can be obtained.

The resistivity of the element isolation region is preferably greaterthan or equal to 1×10¹⁰ Ω·cm, and the concentration of the impurityelement such as oxygen, nitrogen, or carbon is preferably greater thanor equal to 1×10²⁰ Ω·cm⁻³ and less than 4×10²² Ω·cm⁻³.

Crystallinity of the element isolation region is lowered by addition ofthe impurity element; therefore, it can be said that the elementisolation region is made to be amorphous. On the other hand, because theelement region is a crystalline semiconductor layer, in a case where asemiconductor element is formed in the element region, crystallinity ofthe channel formation region is higher than that of the elementisolation region, and high electron field-effect mobility can beobtained as a semiconductor element.

As the impurity element added to the element isolation region, a raregas element such as argon (Ar), neon (Ne), krypton (Kr), or xenon (Xe)may be used. By further addition of such a rare gas element that is anelement having comparatively high mass as well as oxygen, nitrogen, andcarbon, a physical impact on the semiconductor layer can be increased,whereby crystallinity of the element isolation region can be loweredmore effectively.

Next, over the semiconductor layer, mask layers 652 a, 652 b, 652 c, and652 d that cover the element regions 102 a, 102 b, 102 c, and 102 d andthe element isolation regions 651 c and 651 d are formed, and animpurity element 653 that imparts p-type conductivity is added. By theaddition of the impurity element 653 that imparts p-type conductivity,element isolation regions 101 a, 101 b, 101 c, 101 d, 101 e, and 101 f,which are p-type impurity regions, are formed in the semiconductor layer(see FIG. 5B).

Then, over the semiconductor layer, mask layers 654 a, 654 b, 654 c, and654 d that cover the element regions 102 a, 102 b, 102 c, and 102 d andthe element isolation regions 101 a, 101 b, 101 c, 101 d, 101 e, and 101f are formed, and an impurity element 655 that imparts n-typeconductivity is added. By the addition of the impurity element 655 thatimparts n-type conductivity, element isolation regions 656 a and 656 b,which are n-type impurity regions, are formed in the semiconductor layer(see FIG. 5C).

In this embodiment mode, the element isolation region and the elementregion are provided in the continuous semiconductor layer. Accordingly,the element isolation regions 101 a, 101 b, 101 c, 101 d, 101 e, and 101f and the element region 656 a and 656 b that are insulated and isolatedfrom each other by those element isolation regions are contiguous in thesemiconductor layer. Thus, the surface thereof has high flatness and nosteep step.

A mask is removed, a first insulating layer 105 is formed over thesemiconductor layer, and a charge accumulation layer 106 is formed overthe first insulating layer 105.

The first insulating layer 105 is faulted over the highly flatsemiconductor layer; therefore, coverage is good and shape defects arenot easily generated. Accordingly, defects such as leakage current and ashort can be prevented between the charge accumulation layer 106 formedover the first insulating layer 105 and the element region 102 c. Thus,a semiconductor device that is a nonvolatile semiconductor storagedevice of this embodiment mode can be a highly reliable semiconductordevice in which defects such as a short and leakage current between thecharge accumulation layer and the semiconductor layer that are caused bya coverage defect of the semiconductor layer with the first insulatinglayer are prevented.

The first insulating layer 105 can be formed by applying thermaltreatment, plasma treatment, or the like to the semiconductor layer. Forexample, by performance of oxidation treatment, nitridation treatment,or oxynitridation treatment by high density plasma treatment on thesemiconductor layer, the first insulating layer 105 is formed as anoxide film, a nitride film, or an oxynitride film on the semiconductorlayer. It is to be noted that the first insulating layer 105 may also beformed by a plasma CVD method or a sputtering method.

For example, when a semiconductor layer containing Si as a maincomponent is used as the semiconductor layer, and oxidation treatment ornitridation treatment by high density plasma treatment is performed onthe semiconductor layer, a silicon oxide layer or a silicon nitridelayer is formed as the first insulating layer 105. In addition, afterperforming oxidization treatment on the semiconductor layer by highdensity plasma treatment, nitridation treatment may be performed byperforming high density plasma treatment again. In that case, a siliconoxide layer is formed to be in contact with the semiconductor layer anda nitrogen plasma-treated layer is formed on the surface of the siliconoxide layer or in the vicinity of the surface.

Here, the first insulating layer 105 is formed at a thickness of 1 to 10nm, preferably 1 to 5 nm. For example, a silicon oxide layer with athickness of about 3 nm is formed over the surface of the semiconductorlayer by performing oxidation treatment by high density plasma treatmenton the semiconductor layer, and then nitridation treatment by highdensity plasma is performed thereon to form a nitrogen plasma-treatedlayer on the surface of the silicon oxide layer or in the vicinity ofthe surface. Specifically, first, a silicon oxide layer is formed at athickness of 3 to 6 nm on the semiconductor layer by plasma treatmentunder an oxygen atmosphere. Subsequently, by conducting plasma treatmentunder a nitrogen atmosphere, a nitrogen plasma-treated layer containinga high concentration of nitrogen is provided over the surface of thesilicon oxide layer or in the vicinity of the surface. Here, byconducting plasma treatment under a nitrogen atmosphere, a structure isobtained in which 20 to 50 atomic % nitrogen is contained in a regionfrom the surface of the silicon oxide layer to a depth of about 1 nm. Inthe nitrogen plasma-treated layer, silicon containing oxygen andnitrogen (silicon oxynitride) is fanned. At this time, it is preferableto continuously perform oxidation treatment and nitridation treatment byhigh density plasma treatment without exposure to the air. Bycontinuously conducting such high density plasma treatment, mixture ofcontaminants can be prevented and improvement in production efficiencycan be achieved.

In the case of oxidizing the semiconductor layer by high density plasmatreatment, the plasma treatment is conducted under an oxygen atmosphere(e.g., an atmosphere containing oxygen (O₂) or dinitrogen monoxide (N₂O)and a rare gas (containing at least one of He, Ne, Ar, Kr, and Xe), oran atmosphere containing oxygen or dinitrogen monoxide, hydrogen (H₂),and a rare gas). Meanwhile, in the case of nitriding the semiconductorlayer by high density plasma treatment, the plasma treatment isconducted under a nitrogen atmosphere (e.g., an atmosphere containingnitrogen (N₂) and a rare gas (containing at least one of He, Ne, Ar, Kr,and Xe), an atmosphere containing nitrogen, hydrogen, and a rare gas, oran atmosphere containing NH₃ and a rare gas).

As the rare gas, Ar can be used, for example. Alternatively, a mixed gasof Ar and Kr can also be used. In the case of performing high densityplasma treatment under a rare gas atmosphere, the first insulating layer105 may contain the rare gas (which includes at least one of He, Ne, Ar,Kr, and Xe) which has been used for the plasma treatment. For example,when Ar is used, the first insulating layer 105 may contain Ar.

The high density plasma treatment is conducted in the atmospherecontaining the above-described gas, with the conditions of a plasmaelectron density of 1×10¹¹ cm⁻³ or more and a plasma electrontemperature of 1.5 eV or less. Specifically, the plasma treatment isconducted with a plasma electron density greater than or equal to 1×10¹¹cm⁻³ and less than or equal to 1×10¹³ cm⁻³, and a plasma electrontemperature greater than or equal to 0.5 eV and less than or equal to1.5 eV. Since the plasma electron density is high and the electrontemperature in the vicinity of the treatment subject (here, thesemiconductor layer) formed on the substrate 100 is low, plasma damageto the treatment subject can be prevented. In addition, since the plasmaelectron density is as high as 1×10¹¹ cm⁻³ or more, an oxide or nitridefilm which is formed by oxidizing or nitriding the treatment subject byplasma treatment is superior in uniformity of the film thickness or thelike to a film formed by a CVD method, a sputtering method, or the like.Thus, a dense film can be obtained. Further, since the plasma electrontemperature is set as low as 1.5 eV or less, oxidation or nitridationtreatment can be performed at a temperature lower than that of theconventional plasma treatment or thermal oxidation treatment. Forexample, even when the plasma treatment is performed at a temperaturelower than the strain point of a glass substrate by 100° C. or more,oxidation or nitridation treatment can be sufficiently performed. As afrequency for generating plasma, high frequency such as microwaves(e.g., 2.45 GHz) can be used.

In this embodiment mode, in the case of oxidizing a treatment subject byhigh density plasma treatment, a mixed gas of oxygen (O₂), hydrogen(H₂), and argon (Ar) is introduced. The mixed gas used here may beintroduced with an oxygen flow rate of 0.1 to 100 seem, a hydrogen flowrate of 0.1 to 100 sccm, and an argon flow rate of 100 to 5000 sccm. Itis to be noted that the mixed gas is preferably introduced with a ratioof oxygen:hydrogen:argon=1:1:100. For example, the mixed gas may beintroduced with an oxygen flow rate of 5 sccm, a hydrogen flow rate of 5sccm, and an argon flow rate of 500 sccm.

In the case of conducting nitridation by high density plasma treatment,a mixed gas of nitrogen (N₂) and argon (Ar) is introduced. The mixed gasused here may be introduced with a nitrogen flow rate of 20 to 2000 sccmand an argon flow rate of 100 to 10000 sccm. For example, the mixed gasmay be introduced with a nitrogen flow rate of 200 sccm and an argonflow rate of 1000 sccm.

In this embodiment mode, the first insulating layer 105 formed over thesemiconductor layer that is provided in the memory portion serves as atunnel insulating layer of a nonvolatile memory element which iscompleted subsequently. Thus, the thinner the first insulating layer 105is, the easier it will be for tunnel current to flow through the layer,and thus higher-speed operation of the memory can be achieved. Inaddition, the thinner the first insulating layer 105 is, the easier itwill be for charges to be accumulated in a charge accumulation layerthat is formed subsequently, at a low voltage, and thus lower powerconsumption of the semiconductor device can be achieved. Therefore, thefirst insulating layer 105 is preferably formed to be thin.

As a general method for forming a thin insulating layer over asemiconductor layer, there is a thermal oxidation method. However, whena substrate which does not have a sufficiently high melting point suchas a glass substrate is used as the substrate 100, it is very difficultto form the first insulating layer 105 by a thermal oxidation method. Inaddition, an insulating layer formed by a CVD method or a sputteringmethod does not have a sufficient film quality due to its internaldefects, and has a problem in that defects such as pin holes will begenerated when the film is formed to be thin. Further, when aninsulating layer is formed by the CVD method or the sputtering method,the coverage of the ends of the semiconductor layer is not enough, andthere may be a case where a conductive film or the like formed over thefirst insulating layer 105 subsequently is shorted to the semiconductorlayer. Thus, by formation of the first insulating layer 105 by highdensity plasma treatment as shown in this embodiment mode, an insulatinglayer that is denser than an insulating layer formed by a CVD method, asputtering method, or the like can be formed. As a result, high-speedoperation of the memory can be achieved and the charge holdingproperties can be improved. It is to be noted that in the case offorming the first insulating layer 105 by a CVD method or a sputteringmethod, it is preferable to perform high density plasma oxidation,nitridation, or oxynitridation treatment to the surface of theinsulating layer after forming the insulating layer.

The charge accumulation layer 106 serving as a floating gate can beformed using silicon (Si), a silicon compound, germanium (Ge), or agermanium compound. As a silicon compound, silicon nitride, siliconnitride oxide, silicon carbide, silicon germanium which contains 10atomic % or more of germanium, metal nitride, metal oxide or the likecan be used. As a typical example of a germanium compound, silicongermanium can be given, in which case 10 atomic % or more of germaniumis preferably contained with respect to silicon. This is because, if theconcentration of germanium is less than or equal to 10 atomic %, theeffect of the germanium as the constituent element would be small, andthe bandgap of the charge accumulation layer would not becomeeffectively small.

The charge accumulation layer 106 is applied to the semiconductor deviceaccording to the present invention for charge accumulation. However,other materials can be applied as long as the similar function isprovided. For example, a ternary semiconductor containing germanium maybe used, or the semiconductor material may be hydrogenated.Alternatively, as a material having a function of the chargeaccumulation layer of the nonvolatile memory element, the chargeaccumulation layer can be replaced with an oxide or a nitride of thegermanium or the germanium compound.

As a material for forming the charge accumulation layer 106, metalnitride or metal oxide can be used. As metal nitride, tantalum nitride,tungsten nitride, molybdenum nitride, titanium nitride, or the like canbe used. As metal oxide, tantalum oxide, titanium oxide, tin oxide, orthe like can be used.

It is also possible to form the charge accumulation layer 106 to have astacked structure of the above-described materials. When a layer made ofthe above-described silicon, silicon compound, metal nitride, or metaloxide is formed above a layer made of germanium or a germanium compound,the upper layer can be used as a barrier layer for water resistance orchemical resistance in the manufacturing process. Therefore, handling ofthe substrate in photolithography, etching, and washing processesbecomes easier, and thus the productivity can be improved. That is, theprocessing of the charge accumulation layer can be facilitated.

The first insulating layer 105 and the charge accumulation layer 106 areprocessed into desired shapes so that a first insulating layer 107 and acharge accumulation layer 108 are formed over the element region 102 cwhich is used as the memory element (see FIG. 5E). Further, a mask layer120 is formed over the charge accumulation layer 108 and the chargeaccumulation layer 108 is selectively etched using the mask layer 120,thereby forming a charge accumulation layer 109 (see FIG. 5F).

Next, impurity regions are formed in specific regions of the elementregion 102 d. Here, after removing the mask layer 120, mask layers 121 ato 121 f are selectively formed so as to cover the element regions 102 ato 102 c and a part of the element region 102 d. Then, an impurityelement 119 is introduced into a part of the element region 102 d whichis not covered with mask layers 121 a to 121 f so that impurity regions122 a and 122 b are formed (see FIG. 6A). As the impurity element, animpurity element that imparts n-type conductivity or an impurity elementthat imparts p-type conductivity is used. As the n-type impurityelement, phosphorus (P), arsenic (As), or the like can be used. As thep-type impurity element, boron (B), aluminum (Al), gallium (Ga), or thelike can be used. Here, phosphorus (P) is introduced as the impurityelement into the element region 102 d.

Next, a second insulating layer 123 is formed so as to cover the elementregion 102 d and the first insulating layer 107 and the chargeaccumulation layer 109 that are formed above the element region 102 c.

The second insulating layer 123 is formed to have either a single layeror stacked layers by a CVD method, a sputtering method, or the like,using an insulating material such as silicon oxide, silicon nitride,silicon oxynitride (SiO_(x)N_(y)) (x>y>0), or silicon nitride oxide(SiN_(x)O_(y)) (x>y>0). Alternatively, the second insulating layer 123can be formed using aluminum oxide (AlO_(x)), hafnium oxide (HfO_(x)),or tantalum oxide (TaO_(x)). For example, in the case of providing thesecond insulating layer 123 to have a single layer, a silicon oxynitridefilm or a silicon nitride oxide film is formed at a thickness of 5 to 50nm by a CVD method. Meanwhile, in the case of providing the secondinsulating layer 123 to have a three-layer structure, a siliconoxynitride film is formed as a first insulating layer, a silicon nitridefilm is formed as a second insulating layer, and a silicon oxynitridefilm is formed as a third insulating layer. Further, oxide or nitride ofgermanium can be used for the second insulating layer 123.

It is to be noted that the second insulating layer 123 formed above theelement region 102 c serves as a control insulating layer of anonvolatile memory element which is completed subsequently, and thesecond insulating layer 123 formed above the element region 102 d servesas a gate insulating layer of a transistor which is completedsubsequently.

Next, a third insulating layer 135 is formed so as to cover the elementregions 102 a and 102 b.

The third insulating layer 135 is formed by using any of theabove-described methods used for forming the first insulating layer 105.For example, by performance of oxidation treatment, nitridationtreatment, or oxynitridation treatment by high density plasma treatmenton the semiconductor layer including the element isolation regions 101 ato 101 d, the third insulating layer 135 is formed as a silicon oxidefilm, a silicon nitride film, or a silicon oxynitride film on thesemiconductor layer, respectively.

Here, the third insulating layer 135 is formed to a thickness of 1 to 20nm, preferably 1 to 10 nm. For example, a silicon oxide film is formedon the surface of the semiconductor layer including the element regions102 a and 102 b and the element isolation regions 101 a to 101 d byperformance of oxidation treatment by high density plasma treatment onthe semiconductor layer. Then, nitridation treatment by high densityplasma treatment is performed on the silicon oxide film so that asilicon oxynitride film is formed on the surface of the silicon oxidefilm. In this case, the surface of the second insulating layer 123formed above the element regions 102 c and 102 d is also oxidized ornitrided so that an oxide film or an oxynitride film is formed. Thethird insulating layer 135 foamed above the element regions 102 a and102 b serves as a gate insulating layer of transistors which arecompleted subsequently.

Next, a conductive film is formed so as to cover the third insulatinglayer 135 formed above the element regions 102 a and 102 b in thesemiconductor layer and also cover the second insulating layer 123formed above the element regions 102 c and 102 d. Here, an example isshown where a first conductive film and a second conductive film aresequentially stacked as the conductive film. Needless to say, theconductive film may be formed to have a single layer or a stackedstructure of three layers or more.

The first conductive film and the second conductive film can be formedusing an element selected from tantalum (Ta), tungsten (W), titanium(Ti), molybdenum (Mo), aluminum (Ai), copper (Cu), chromium (Cr),niobium (Nb), and the like, or an alloy material or a compound materialcontaining such an element as a main component. Alternatively, a metalnitride film obtained by nitriding the above-described metal can beused. Further, a semiconductor material typified by polycrystallinesilicon doped with an impurity element such as phosphorus can also beused.

Here, a stacked structure is provided such that the first conductivefilm is formed using tantalum nitride and the second conductive film isstacked thereover using tungsten. Alternatively, the first conductivefilm may be formed as either a single-layer film or a stacked film usingtungsten nitride, molybdenum nitride, and/or titanium nitride, and thesecond conductive film may also be formed as either a single-layer filmor a stacked film using tantalum, molybdenum, and/or titanium.

Next, the first and second conductive films which are stacked areselectively etched to be removed so that the first conductive film andthe second conductive film remain above a part of the element regions102 a to 102 d in the semiconductor layer. Thus, first conductive layers124 a to 124 d and second conductive layers 125 a to 125 d which serveas gate electrode layers are formed (see FIG. 6B). It is to be notedthat the first conductive layer 124 c and the second conductive layer125 c formed above the element region 102 c which is provided in thememory portion serve as control gate electrode layers of a nonvolatilememory element which is completed subsequently. In addition, the firstconductive layers 124 a, 124 b, and 124 d and the second conductivelayers 125 a, 125 b, and 125 d serve as gate electrode layers oftransistors which are completed subsequently.

Next, mask layers 126 a to 126 e are selectively formed so as to coverthe element regions 102 a, 102 c, and 102 d. Then, an impurity element127 is introduced into the element region 102 b, using the mask layers126 a to 126 e, the first conductive layer 124 b, and the secondconductive layer 125 b as masks, thereby forming impurity regions (seeFIG. 6C). As the impurity element, an impurity element that impartsn-type conductivity or an impurity element that imparts p-typeconductivity is used. As the n-type impurity element, phosphorus (P),arsenic (As), or the like can be used. As the p-type impurity element,boron (B), aluminum (Al), gallium (Ga), or the like can be used. Here,an impurity element (e.g., boron (B)) having a conductivity typeopposite to that of the impurity element which has been introduced intothe element region 102 d in FIG. 6A is introduced. As a result,high-concentration impurity regions 132 a and 132 b which form a sourceregion and a drain region and a channel formation region 134 are formed.

Next, mask layers 128 a to 128 g are selectively formed so as to coverthe element region 102 b. Then, an impurity element 129 is introducedinto the element regions 102 a, 102 c, and 102 d, using the mask layers128 a to 128 g, the first conductive layers 124 a, 124 c, and 124 d, andthe second conductive layers 125 a, 125 c, and 125 d as masks, therebyforming impurity regions (see FIG. 6D). As the impurity element, animpurity element that imparts n-type conductivity or an impurity elementthat imparts p-type conductivity is used. As the n-type impurityelement, phosphorus (P), arsenic (As), or the like can be used. As thep-type impurity element, boron (B), aluminum (Al), gallium (Ga), or thelike can be used. Here, phosphorus (P) is used as the impurity element.

In FIG. 6D, by introduction of the impurity element 129,high-concentration impurity regions 130 a and 130 b which form a sourceregion and a drain region and a channel formation region 135 a areformed in the element region 102 a. In the element region 102 c,high-concentration impurity regions 130 c and 130 d which form a sourceregion and a drain region, low-concentration impurity regions 131 a and131 b which form LDD regions, and a channel formation region 135 b areformed. In the element region 102 d, high-concentration impurity regions130 e and 130 f which form a source region and a drain region,low-concentration impurity regions 131 c and 131 d which form LDDregions, and a channel formation region 135 c are formed.

The low-concentration impurity regions 131 a and 131 b formed in theelement region 102 c are formed by an impurity element introduced inFIG. 6D which has passed through the charge accumulation layer 109serving as the floating gate. Thus, the channel formation region 135 bis formed in a region of the element region 102 c which overlaps withboth of the second conductive layer 125 c and the charge accumulationlayer 109; the low-concentration impurity regions 131 a and 131 b arefaulted in a region of the element region 102 c which overlaps with thecharge accumulation layer 109 but does not overlap with the secondconductive layer 125 c; and the high-concentration impurity regions 130c and 130 d are formed in a region of the element region 102 c whichoverlaps with neither the charge accumulation layer 109 nor the secondconductive layer 125 c.

Next, an insulating layer 133 is formed so as to cover the secondinsulating layer 123, the third insulating layer 135, the firstconductive layers 124 a to 124 d, and the second conductive layers 125 ato 125 d. Then, wiring layers 136 a to 136 h, which are electricallyconnected to the high-concentration impurity regions 130 a to 130 f, 132a, and 132 b formed in the element regions 102 a to 102 d, are formedover the insulating layer 133 (see FIG. 6E).

The insulating layer 133 can be formed to have either a single layer ora stacked structure by a CVD method, a sputtering method, or the like,using an insulating layer containing oxygen or nitrogen such as siliconoxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride(SiO_(x)N_(y)) (x>y>0), or silicon nitride oxide (SiN_(x)O_(y)) (x>y>0);a film containing carbon such as DLC (diamond-like carbon); an organicmaterial such as epoxy, polyimide, polyamide, polyvinyl phenol,benzocyclobutene, or acrylic; and/or a siloxane material such as asiloxane resin.

The wiring layers 136 a to 136 h are faulted to have either a singlelayer or stacked layers by a CVD method, a sputtering method, or thelike, using an element selected from aluminum (Al), tungsten (W),titanium (Ti), tantalum (Ta), molybdenum (Mo), nickel (Ni), platinum(Pt), copper (Cu), gold (Au), silver (Ag), manganese (Mn), neodymium(Nd), carbon (Cu), and silicon (Si), or an alloy material or a compoundmaterial containing such an element as a main component. An alloymaterial containing aluminum as a main component corresponds to, forexample, a material containing aluminum as a main component and alsocontaining nickel, or an alloy material containing aluminum as a maincomponent and also containing nickel and one or both of carbon andsilicon. The wiring layers 136 a to 136 h are preferably formed to havea stacked structure of a barrier film, an aluminum silicon (Al—Si) film,and a barrier film, or a stacked structure of a barrier film, analuminum silicon (Al—Si) film, a titanium nitride (TiN) film, and abarrier film. It is to be noted that the barrier film corresponds to athin film made of titanium, a nitride of titanium, molybdenum, or anitride of molybdenum. Aluminum and aluminum silicon, which have lowresistance values and are inexpensive, are most suitable for thematerial of the wiring layers 136 a to 136 h. In addition, when thebarrier layers are provided as the top layer and the bottom layer,generation of hillocks of aluminum or aluminum silicon can be prevented.Further, when a barrier film made of titanium which is an element havingan excellent reducing property is used, even if a thin natural oxidefilm is formed on the crystalline semiconductor layer, the natural oxidefilm can be chemically reduced and thus an excellent contact between thebarrier film and the crystalline semiconductor layer can be obtained.

Therefore, with the use of the present invention, a semiconductor layercan be isolated into a plurality of element regions without beingdivided into island shapes, and steps resulting from the edge portion ofthe semiconductor layer are not generated. Thus, an insulating layer canbe formed over a flat semiconductor layer, and the coverage of thesemiconductor layer with the insulating layer can be improved.Therefore, a semiconductor device that is a highly reliablesemiconductor storage device in which defects such as a short andleakage current between a charge accumulation layer, a control gateelectrode layer, a gate electrode layer, and a semiconductor layer thatare caused by a coverage defect of the semiconductor layer with aninsulating layer are prevented and a manufacturing method of such asemiconductor device can be provided. Accordingly, furtherminiaturization and higher integration of the semiconductor devicehaving memory elements are possible, and higher performance of thesemiconductor device can be achieved. In addition, because defects suchas shape defects of the film can be reduced, in the manufacturingprocess, the semiconductor device can be manufactured with good yield.

This embodiment mode can be freely implemented in combination with anyof the other embodiment modes.

Embodiment Mode 8

In this embodiment mode, examples of other highly reliable semiconductordevices having a CMOS circuit and a memory element, in which defectssuch as a short and leakage current between a gate electrode layer and asemiconductor layer that are caused by a coverage defect of asemiconductor layer with an insulating layer in a semiconductor elementare prevented, will be described with reference to drawings. Amanufacturing method of a semiconductor device in this embodiment modewill be described in detail with reference to FIGS. 7A to 7F and FIGS.8A to 8E. This embodiment mode shows a semiconductor device in whichshapes of a gate electrode layer and a control gate electrode layerdiffer from those in the semiconductor device in Embodiment Mode 7. Itis to be noted that in a case where the same portions as the aboveembodiment mode are denoted, explanation thereof will be omitted.

A stack of an insulating layer 112 a and an insulating layer 112 bserving as a base film is faulted as a base film over a substrate 100having an insulating surface.

Next, a semiconductor layer 150 is formed over the base film. Thesemiconductor layer 150 may be formed at a thickness of 25 to 200 nm(preferably, 30 to 150 nm) by various methods (e.g., a sputteringmethod, an LPCVD method, or a plasma CVD method). In this embodimentmode, it is preferable to use a crystalline semiconductor layer which isobtained by crystallizing an amorphous semiconductor layer by laser.

The thusly obtained semiconductor layer may be doped with a small amountof an impurity element (e.g., boron or phosphorus) in order to controlthe threshold voltage of thin film transistors. Alternatively, suchdoping with the impurity element may be conducted before the step ofcrystallizing the amorphous semiconductor layer. When the amorphoussemiconductor layer is doped with an impurity element and then thermaltreatment is conducted in order to crystallize the amorphoussemiconductor layer, the thermal treatment can also activate theimpurity element. In addition, defects caused in doping can be remedied.

A mask is removed, and a first insulating layer 105 is formed over thesemiconductor layer 150.

The first insulating layer 105 can be formed by applying thermaltreatment, plasma treatment, or the like to the semiconductor layer. Forexample, by performance of oxidation treatment, nitridation treatment,or oxynitridation treatment by high density plasma treatment on thesemiconductor layer, the first insulating layer 105 is formed as anoxide film, a nitride film, or an oxynitride film on the semiconductorlayer. It is to be noted that the first insulating layer 105 may also beformed by a plasma CVD method or a sputtering method.

For example, when a semiconductor layer containing Si as a maincomponent is used as the semiconductor layer, and oxidation treatment ornitridation treatment by high density plasma is performed on thesemiconductor layer, a silicon oxide layer or a silicon nitride layer isformed as the first insulating layer 105. In addition, after performingoxidization treatment on the semiconductor layer by high density plasmatreatment, nitridation treatment may be performed by performing highdensity plasma treatment again. In that case, a silicon oxide layer isformed to be in contact with the semiconductor layer and a nitrogenplasma-treated layer is formed on the surface of the silicon oxide layeror in the vicinity of the surface.

Here, the first insulating layer 105 is formed at a thickness of 1 to 10nm, preferably 1 to 5 nm. For example, a silicon oxide layer with athickness of about 3 nm is formed over the surface of the semiconductorlayer by performing oxidation treatment by high density plasma on thesemiconductor layer, and then nitridation treatment by high densityplasma is performed thereon to form a nitrogen plasma-treated layer onthe surface of the silicon oxide layer or in the vicinity of thesurface. Specifically, first, a silicon oxide layer is formed at athickness of 3 to 6 nm on the semiconductor layer by plasma treatmentunder an oxygen atmosphere. Subsequently, by conducting plasma treatmentunder a nitrogen atmosphere, a nitrogen plasma-treated layer containinga high concentration of nitrogen is provided over the surface of thesilicon oxide layer or in the vicinity of the surface. Here, byconducting plasma treatment under a nitrogen atmosphere, a structure isobtained in which 20 to 50 atomic % nitrogen is contained in a regionfrom the surface of the silicon oxide layer to a depth of about 1 nm. Inthe nitrogen plasma-treated layer, silicon containing oxygen andnitrogen (silicon oxynitride) is formed. At this time, it is preferableto continuously perform oxidation treatment and nitridation treatment byhigh density plasma without exposure to the air. By continuouslyconducting such high density plasma treatment, mixture of contaminantscan be prevented and improvement in production efficiency can beachieved.

In this embodiment mode, the first insulating layer 105 formed over thesemiconductor layer that is provided in the memory portion serves as atunnel insulating layer of a nonvolatile memory element which iscompleted subsequently. Thus, the thinner the first insulating layer 105is, the easier it will be for tunnel current to flow through the layer,and thus higher-speed operation of the memory can be achieved. Inaddition, the thinner the first insulating layer 105 is, the easier itwill be for charges to be accumulated in a charge accumulation layerthat is formed subsequently, at a low voltage, and thus lower powerconsumption of the semiconductor device can be achieved. Therefore, thefirst insulating layer 105 is preferably formed to be thin.

An impurity element is selectively added to the semiconductor layer thatis a crystalline semiconductor layer through the first insulation layer105 to form an element isolation region. The semiconductor layer isisolated into a plurality of element regions by the element isolationregion. Over the semiconductor layer, mask layers 103 a, 103 b, 103 c,and 103 d are formed, and an impurity element 104 that does notcontribute to conductivity is added. By the addition of the impurityelement 104 that does not contribute to conductivity, element isolationregions 651 a, 651 b, 651 c, 651 d, 651 e, 651 f, 651 g, and 651 h andelement regions 102 a, 102 b, 102 c, and 102 d that are insulated andisolated from each other by those element isolation region are formed(see FIG. 7B).

Next, over the semiconductor layer, mask layers 652 a, 652 b, 652 c, and652 d that cover the element regions 102 a, 102 b, 102 c, and 102 d andthe element isolation regions 651 c and 651 d are formed, and animpurity element 653 that imparts p-type conductivity is added throughthe first insulating layer 105. By the addition of the impurity element653 that imparts p-type conductivity, element isolation regions 101 a,101 b, 101 c, 101 d, 101 e, and 101 f that are p-type impurity regionsare formed in the semiconductor layer (see FIG. 7C).

Next, over the semiconductor layer, mask layers 654 a, 654 b, 654 c, and654 d that cover the element regions 102 a, 102 b, 102 c, and 102 d andthe element isolation regions 101 a, 101 b, 101 c, 101 d, 101 e, and 101f are formed, and an impurity element 655 that imparts n-typeconductivity is added through the first insulating layer 105. By theaddition of the impurity element 655 that imparts n-type conductivity,element isolation regions 656 a and 656 b that are n-type impurityregions are formed in the semiconductor layer (see FIG. 7D).

In this embodiment mode, the element isolation region and the elementregion are provided in the continuous semiconductor layer. Accordingly,the element isolation regions 101 a, 101 b, 101 c, 101 d, 101 e, and 101f and the element isolation regions 656 a and 656 b and the elementregions 102 a, 102 b, 102 c, and 102 d that are insulated and isolatedfrom each other by the element isolation regions are contiguous in thesemiconductor layer. Thus, the surface thereof has high flatness and nosteep step.

Since an impurity element is added to the semiconductor layer 150through the first insulating layer 105 by a doping method or the like,physical energy in adding the impurity element can be controlled.Therefore, the energy in adding can be decreased to a level that doesnot cause damage or the like to the semiconductor layer, and thecrystallinity of the semiconductor layer can be selectively lowered toform element isolation regions. It is also possible to once remove thefirst insulating layer 105 after forming the element isolation regionsand the element regions by introduction of an impurity element and thenform the first insulating layer 105 again. Further, plasma treatment maybe performed on the insulating layer which is formed again so that thesurface becomes densified.

The element isolation region is formed by selective addition of a firstimpurity element that does not contribute to conductivity and a secondimpurity element that imparts an opposite conductivity type to that of asource region and a drain region in the element region in order toelectrically isolate elements from each other in one semiconductorlayer.

As the first impurity element that does not contribute to conductivity,an impurity element of at least one or more kinds of oxygen, nitrogen,and carbon can be used. The element isolation region to which the firstimpurity element is added, conductivity is lowered by mixture of thefirst impurity element that does not contribute to conductivity, andresistance of the element isolation region is increased because itscrystallinity is lowered by a physical impact (it can also be referredto as a so-called sputtering effect) on the semiconductor layer atadding. In the element isolation region with the increased resistance,electron field-effect mobility is also lowered, and accordingly,elements can be electrically isolated from each other. On the otherhand, in a region to which an impurity element is not added, electronfield-effect mobility that is high enough to be able to serve as anelement is kept, and accordingly, the region can be used as an elementregion.

The element region has a source region, a drain region, and a channelformation region. The source region and the drain region are impurityregions having one conductivity type (for example, n-type impurityregions or p-type impurity regions). An impurity element that imparts anopposite conductivity type to that of the source region and the drainregion in the element region is added to the element isolation region,whereby the element isolation region is made to be an impurity regionhaving an opposite conductivity type to that of the source region andthe drain region in the element region that is adjacent to the elementisolation region. That is, in a case where the source region and thedrain region in the element region are n-type impurity regions, theadjacent element isolation region may be formed as a p-type impurityregion. Similarly, in a case where the source region and the drainregion in the element region are p-type impurity regions, the adjacentelement isolation region may be formed as an n-type impurity region. Theelement region and the element isolation region that are adjacent toeach other form a PN junction. Accordingly, the element regions can befurther insulated and isolated from each other by the element isolationregion provided between the element regions.

One feature of the present invention is that one semiconductor layer isisolated into a plurality of element regions in the manner thatresistance of the element isolation region by which the element regionsare insulated and isolated from each other is increased by addition ofthe first impurity element that does not contribute to conductivity, andfurther, a PN junction is formed in a position where the element regionand the element isolation region are in contact with each other byaddition of the second impurity element that imparts an oppositeconductivity type to that of the source region and the drain region inthe element region. By the present invention, the element regions can beisolated from each other by an effect caused by each of the firstimpurity element and the second impurity element. Thus, a higher effectof insulation and isolation of the element can be obtained.

The resistivity of the element isolation region is preferably greaterthan or equal to 1×10¹⁰ Ω·cm, and the concentration of the impurityelement such as oxygen, nitrogen, or carbon is preferably greater thanor equal to 1×10²⁰ Ω·cm⁻³ and less than 4×10²² Ω cm⁻³.

Crystallinity of the element isolation region is lowered by addition ofthe impurity element; therefore, it can be said that the elementisolation region is made to be amorphous. On the other hand, because theelement region is a crystalline semiconductor layer, in a case where asemiconductor element is fanned in the element region, crystallinity ofthe channel formation region is higher than that of the elementisolation region, and high electron field-effect mobility can beobtained as a semiconductor element.

As the impurity element added to the element isolation region, a raregas element such as argon (Ar), neon (Ne), krypton (Kr), or xenon (Xe)may be used. By further addition of such a rare gas element that is anelement having comparatively high mass as well as oxygen, nitrogen, andcarbon, a physical impact on the semiconductor layer can be increased,whereby crystallinity of the element isolation region can be loweredmore effectively.

The first insulating layer 105 is fainted over the highly flatsemiconductor layer; therefore, coverage is good and shape defects arenot easily generated. Accordingly, defects such as leakage current and ashort can be prevented between the charge accumulation layer 106 formedover the first insulating layer 105 and the element region 102 c. Thus,a semiconductor device that is a nonvolatile semiconductor storagedevice of this embodiment mode can be a highly reliable semiconductordevice in which defects such as a short and leakage current between thecharge accumulation layer and the semiconductor layer that are caused bya coverage defect of the semiconductor layer with the first insulatinglayer are prevented.

A charge accumulation layer 106 is formed over the first insulatinglayer 105 (see FIG. 7E).

The charge accumulation layers 271, 281, and 291 can be formed usingtypically silicon, a silicon compound, germanium, or a germaniumcompound as a semiconductor material forming the charge accumulationlayers 271, 281, and 291. As a silicon compound, silicon nitride,silicon nitride oxide, silicon carbide, silicon germanium containinggermanium at a concentration of greater than or equal to 10 atomic %,metal nitride, metal oxide, or the like can be used. Silicon germaniumis a typical example of a germanium compound, and in this case, it ispreferable that germanium be contained at a concentration of greaterthan or equal to 10 atomic % with respect to silicon. This is because,if the concentration of germanium is less than or equal to 10 atomic %,the effect of the germanium as the constituent element would be small,and the bandgap of the charge accumulation layer would not becomeeffectively small.

The charge accumulation layer 106 is applied to a semiconductor deviceaccording to the present invention for charge accumulation. However,other materials can be applied as long as the similar function isprovided. For example, a ternary system semiconductor includinggermanium may be used. In addition, the semiconductor material may behydrogenated. Further, as a layer having a function as a chargeaccumulation layer of a nonvolatile memory element, the chargeaccumulation layer can be replaced with an oxide or a nitride of thegermanium or a germanium compound.

Further, metal nitride or metal oxide can be used as a material formingthe charge accumulation layer 106. As metal nitride, tantalum nitride,tungsten nitride, molybdenum nitride, titanium nitride, or the like canbe used. As metal oxide, tantalum oxide, titanium oxide, tin oxide, orthe like can be used.

Further, the charge accumulation layer 106 may be formed using a stackedstructure of the material as described above. When a layer of silicon ora silicon compound, or metal nitride or metal oxide as described aboveis provided on the upper layer side of the layer formed using germaniumor a germanium compound, the layer can be used as a barrier layer forwater resistance or chemical resistance in the manufacturing process.Therefore, the substrate can be easily handled in a photolithographystep, an etching step, or a cleaning step, whereby productivity can beimproved. In other words, the charge accumulation layer can be easilyprocessed.

The first insulating layer 105 and the charge accumulation layer 106 areprocessed into desired shapes to form a first insulating layer 107 and acharge accumulation layer 108 over the element region 102 c which isused as the memory element (see FIG. 7F). Further, a mask layer 120 isformed over the charge accumulation layer 108 and the chargeaccumulation layer 108 is selectively etched using the mask layer 120,thereby forming a charge accumulation layer 109 (see FIG. 8A).

Next, a second insulating layer 123 is formed so as to cover the firstinsulating layer 107 and the charge accumulation layer 109 formed abovethe element region 102 d and the element region 102 c.

It is to be noted that the second insulating layer 123 formed above theelement region 102 c serves as a control insulating layer of anonvolatile memory element which is completed subsequently, and thesecond insulating layer 123 formed above the element region 102 d servesas a gate insulating layer of a transistor which is completedsubsequently.

Next, a third insulating layer 135 is formed so as to cover the elementregions 102 a and 102 b.

Next, a conductive film is formed so as to cover the third insulatinglayer 135 formed above the element regions 102 a and 102 b in thesemiconductor layer and also cover the second insulating layer 123formed above the element regions 102 c and 102 d. Here, an example isshown where a first conductive film and a second conductive film aresequentially stacked as the conductive film. Needless to say, theconductive film may be formed to have a single layer or a stackedstructure of three layers or more.

Next, the first and second conductive films which are stacked areselectively etched and removed so that the first conductive film and thesecond conductive film remain above a part of the element regions 102 ato 102 d in the semiconductor layer. Thus, first conductive layers 154 ato 154 d and second conductive layers 155 a to 155 d which serve as gateelectrode layers are formed (see FIG. 8B). It is to be noted that thefirst conductive layer 154 c and the second conductive layer 155 cformed above the element region 102 c which is provided in the memoryportion serve as control gate electrode layers of a nonvolatile memoryelement which is completed subsequently. Further, the first conductivelayers 154 a, 154 b, and 154 d and the second conductive layers 155 a,155 b, and 155 d serve as gate electrode layers of transistors which arecompleted subsequently.

Next, mask layers 156 a to 156 e are selectively formed so as to coverthe element regions 102 a, 102 c, and 102 d. Then, an impurity element157 is introduced into the element region 102 b, using the mask layers156 a to 156 e, the first conductive layer 154 b, and the secondconductive layer 155 b as masks, thereby forming impurity regions (seeFIG. 8C). As the impurity element, an impurity element that impartsn-type conductivity or an impurity element that imparts p-typeconductivity is used. As the n-type impurity element, phosphorus (P),arsenic (As), or the like can be used. As the p-type impurity element,boron (B), aluminum (Al), gallium (Ga), or the like can be used. Here,an impurity element (e.g., boron (B)) is introduced. As a result,high-concentration impurity regions 162 a and 162 b which form a sourceregion and a drain region, low-concentration impurity regions 164 a and164 b which form LDD regions, and a channel formation region 165 areformed in the element region 102 b.

Next, mask layers 158 a to 158 g are selectively formed so as to coverthe element region 102 b. Then, an impurity element 159 is introducedinto the element regions 102 a, 102 c, and 102 d, using the mask layers158 a to 158 g, the first conductive layers 154 a, 154 c, and 154 d, andthe second conductive layers 155 a, 155 c, and 155 d as masks, therebyfanning impurity regions (see FIG. 8D). As the impurity element, animpurity element that imparts n-type conductivity or an impurity elementthat imparts p-type conductivity is used. As the n-type impurityelement, phosphorus (P), arsenic (As), or the like can be used. As thep-type impurity element, boron (B), aluminum (Al), gallium (Ga), or thelike can be used. Here, phosphorus (P) is used as the impurity element.

In FIG. 8D, by introduction of the impurity element, high-concentrationimpurity regions 160 a and 160 b which form a source region and a drainregion, low-concentration impurity regions 161 e and 161 f which formLDD regions, and a channel formation region 167 a are formed in theelement region 102 a. In the element region 102 c, high-concentrationimpurity regions 160 c and 160 d which form a source region and a drainregion, low-concentration impurity regions 161 a and 161 b which formLDD regions, and a channel formation region 167 b are formed. In theelement region 102 d, high-concentration impurity regions 160 e and 160f which form a source region and a drain region, low-concentrationimpurity regions 161 c and 161 d which form LDD regions, and a channelformation region 167 c are formed.

Next, an insulating layer 163 is formed so as to cover the secondinsulating layer 123, the third insulating layer 135, the firstconductive layers 154 a to 154 d, and the second conductive layers 155 ato 155 d. Then, wiring layers 166 a to 166 h, which are electricallyconnected to the high-concentration impurity regions 160 a to 160 f, 162a, and 162 b formed in the element regions 102 a to 102 d, are formedover the insulating layer 163 (see FIG. 8E).

Therefore, with the use of the present invention, a semiconductor layercan be isolated into a plurality of element regions without beingdivided into island shapes, and steps resulting from the edge portion ofthe semiconductor layer are not generated.

Thus, an insulating layer can be formed over a flat semiconductor layer,and the coverage of the semiconductor layer with the insulating layercan be improved. Therefore, a semiconductor device that is a highlyreliable semiconductor storage device in which defects such as a shortand leakage current between a charge accumulation layer, a control gateelectrode layer, a gate electrode layer, and a semiconductor layer thatare caused by a coverage defect of the semiconductor layer with aninsulating layer are prevented and a manufacturing method of such asemiconductor device can be provided. Accordingly, furtherminiaturization and higher integration of the semiconductor device arepossible, and higher performance of the semiconductor device can beachieved. In addition, because defects such as shape defects of the filmcan be reduced, in the manufacturing process, the semiconductor devicecan be manufactured with good yield.

This embodiment mode can be implemented by being combined with otherembodiment modes disclosed in this specification.

Embodiment Mode 9

In this embodiment mode, an example of a highly reliable semiconductordevice having a CMOS circuit and a memory element, in which defects suchas a short and leakage current between a gate electrode layer and asemiconductor layer that are caused by a coverage defect of asemiconductor layer with an insulating layer in a semiconductor elementare prevented, will be described with reference to drawings. Amanufacturing method of a semiconductor device in this embodiment modewill be described in detail with reference to FIGS. 9A to 9C and FIGS.10A to 10C. This embodiment mode shows a semiconductor device differentfrom the semiconductor device in Embodiment Mode 7 in shapes of a firstinsulating layer and a second insulating layer. It is to be noted thatthe same reference numerals are used in a case where the same portionsas the above embodiment mode are denoted, and explanation will beomitted.

In Embodiment Mode 9, a semiconductor device having a CMOS circuit and amemory element in this embodiment mode is manufactured to the stageshown in FIG. 6B.

As shown in FIG. 9A, mask layers 170 a, 170 b, 170 c, 170 d, and 170 eare selectively formed so as to cover the element regions 102 a, 102 cand 102 d, and an impurity element 171 is introduced into the elementregion 102 b using the mask layers 170 a to 170 e, the first conductivelayer 154 b, and the second conductive layer 155 b as masks to formimpurity regions (see FIG. 9A). As the impurity element, an impurityelement that imparts n-type conductivity or an impurity element thatimparts p-type conductivity is used. As the impurity element thatimparts n-type conductivity, phosphorus (P), arsenic (As), or the likecan be used. As the impurity element that imparts p-type that impartsn-type conductivity, boron (B), aluminum (Al), gallium (Ga), or the likecan be used. Here, the impurity element (for example, boron (B)) isintroduced. As a result, impurity regions 172 a and 172 b are formed inthe element region 102 b.

Next, mask layers 173 a, 173 b, 173 c, 173 d, 173 e, 713 f, and 173 gare selectively formed so as to cover the element region 102 b, and animpurity element 174 is introduced into the element regions 102 a, 102c, and 102 d using the mask layers 173 a to 173 g, the first conductivelayers 154 a, 154 c, and 154 d, and the second conductive layers 155 a,155 c, and 155 d as masks to form impurity regions (see FIG. 9B). As theimpurity element, an impurity element that imparts n-type conductivityor an impurity element that imparts p-type conductivity is used. As theimpurity element that imparts n-type conductivity, phosphorus (P),arsenic (As), or the like can be used. As the impurity element thatimparts p-type conductivity, boron (B), aluminum (Al), gallium (Ga), orthe like can be used. Here, phosphorus (P) is used as the impurityelement.

In FIG. 9B, impurity regions 175 a and 175 b are formed in the elementregion 102 a by the introduction of the impurity element 174. Further,impurity regions 175 c and 175 d are framed in the element region 102 c.Furthermore, impurity regions 175 e and 175 f are formed in the elementregion 102 d.

Next, a first insulating layer 107, a second insulating layer 123, and athird insulating layer 135 are selectively etched using the firstconductive layers 154 a to 154 d and the second conductive layers 155 ato 155 d as masks to form insulating layers 188 a and 188 b andinsulating layers 189 a, 189 b, and 189 c. Insulating layers (alsoreferred to as sidewalls) 176 a, 176 b, 176 c, 176 d, 176 e, 176 f, 176g, and 176 h that are in contact with side surfaces of the firstconductive layers 154 a to 154 d, the second conductive layers 155 a to155 d, a charge accumulation layer 109, the insulating layers 188 a and188 b, and the insulating layers 189 a to 189 c are formed.

As shown in FIG. 10A, mask layers 178 a, 178 b, 178 c, 178 d, and 178 eare selectively formed so as to cover the element regions 102 a, 102 cand 102 d, and an impurity element 179 is introduced into the elementregion 102 b using the mask layers 178 a to 178 e, the first conductivelayer 154 b, the second conductive layer 155 b, and the insulatinglayers 176 c, 176 d, and 189 a as masks to form impurity regions (seeFIG. 10A). As the impurity element, an impurity element that impartsn-type conductivity or an impurity element that imparts p-typeconductivity is used. As the impurity element that imparts n-typeconductivity, phosphorus (P), arsenic (As), or the like can be used. Asthe impurity element that imparts p-type conductivity, boron (B),aluminum (Al), gallium (Ga), or the like can be used. Here, the impurityelement (for example, boron (B)) is introduced. As a result,high-concentration impurity regions 180 a and 180 b forming a sourceregion and a drain region, low-concentration impurity regions 187 a and187 b forming LDD regions, and a channel formation region 169 are formedin the element region 102 b.

Next, mask layers 181 a, 181 b, 181 c, 181 d, 181 e, 181 f, and 181 gare selectively formed so as to cover the element region 102 b, and animpurity element 182 is introduced into the element regions 102 a, 102c, and 102 d using the mask layers 181 a to 181 g, the first conductivelayers 154 a, 154 c, and 154 d, the second conductive layers 155 a, 155c, and 155 d, and the insulating layers 176 a, 176 b, 176 e, 176 f, 176g, and 176 h as masks to form impurity regions (see FIG. 10B). As theimpurity element, an impurity element that imparts n-type conductivityor an impurity element that imparts p-type conductivity is used. As theimpurity element that imparts n-type conductivity, phosphorus (P),arsenic (As), or the like can be used. As the impurity element thatimparts p-type conductivity, boron (B), aluminum (Al), gallium (Ga), orthe like can be used. Here, phosphorus (P) is used as the impurityelement.

In FIG. 10B, by the introduction of the impurity element,high-concentration impurity regions 183 a and 183 b forming a sourceregion and a drain region, low-concentration impurity regions 184 a and184 b forming LDD regions, and a channel formation region 198 a areformed in the element region 102 a. Further, high-concentration impurityregions 183 c and 183 d forming a source region and a drain region,low-concentration impurity regions 184 c and 184 d forming LDD regions,and a channel formation region 198 b are formed in the element region102 c. Furthermore, high-concentration impurity regions 183 e and 183 fforming a source region and a drain region, low-concentration impurityregions 184 e and 184 f forming LDD regions, and a channel formationregion 198 c are formed in the element region 102 d.

Then, insulating layers 199 and 186 are formed so as to cover the firstconductive layers 154 a to 154 d, the second conductive layers 155 a to155 d, and the insulating layers 176 a to 176 h. Over the insulatinglayers 199 and 186, wiring layers 185 a, 185 b, 185 c, 185 d, 185 e, 185f, 185 g, and 185 h that are electrically connected to thehigh-concentration impurity regions 183 a to 183 f, 180 a and 180 b thatare formed in the element regions 102 a, 102 b, 102 c, and 102 d areformed (see FIG. 10C).

Also in the semiconductor element in this embodiment mode, an elementisolation region including first and second impurity elements is formedin the semiconductor layer, and element regions in which elementisolation is performed are used.

The element isolation region is formed by selective addition of a firstimpurity element that does not contribute to conductivity and a secondimpurity element that imparts an opposite conductivity type to that of asource region and a drain region in the element region in order toelectrically isolate elements from each other in one semiconductorlayer.

As the first impurity element that does not contribute to conductivity,an impurity element of at least one or more kinds of oxygen, nitrogen,and carbon can be used. The element isolation region to which the firstimpurity element is added, conductivity is lowered by mixture of thefirst impurity element that does not contribute to conductivity, andresistance of the element isolation region is increased because itscrystallinity is lowered by a physical impact (it can also be referredto as a so-called sputtering effect) on the semiconductor layer atadding. In the element isolation region with the increased resistance,electron field-effect mobility is also lowered, and accordingly,elements can be electrically isolated from each other. On the otherhand, in a region to which an impurity element is not added, electronfield-effect mobility that is high enough to be able to serve as anelement is kept, and accordingly, the region can be used as an elementregion.

The element region has a source region, a drain region, and a channelformation region. The source region and the drain region are impurityregions having one conductivity type (for example, n-type impurityregions or p-type impurity regions).

An impurity element that imparts an opposite conductivity type to thatof the source region and the drain region in the element region is addedto the element isolation region, whereby the element isolation region ismade to be an impurity region having an opposite conductivity type tothat of the source region and the drain region in the element regionthat is adjacent to the element isolation region. That is, in a casewhere the source region and the drain region in the element region aren-type impurity regions, the adjacent element isolation region may beformed as a p-type impurity region. Similarly, in a case where thesource region and the drain region in the element region are p-typeimpurity regions, the adjacent element isolation region may be formed asan n-type impurity region. The element region and the element isolationregion that are adjacent to each other faun a PN junction. Accordingly,the element regions can be further insulated and isolated from eachother by the element isolation region provided between the elementregions.

One feature of the present invention is that one semiconductor layer isisolated into a plurality of element regions in the manner thatresistance of the element isolation region by which the element regionsare insulated and isolated from each other is increased by addition ofthe first impurity element that does not contribute to conductivity, andfurther, a PN junction is formed in a position where the element regionand the element isolation region are in contact with each other byaddition of the second impurity element that imparts an oppositeconductivity type to that of the source region and the drain region inthe element region. By the present invention, the element regions can beisolated from each other by an effect caused by each of the firstimpurity element and the second impurity element. Thus, a higher effectof insulation and isolation of the element can be obtained.

The resistivity of the element isolation region is preferably greaterthan or equal to 1×10¹⁰ Ω·cm, and the concentration of the impurityelement such as oxygen, nitrogen, or carbon is preferably greater thanor equal to 1×10²⁰ Ω·cm⁻³ and less than 4×10²² Ω·cm⁻³.

Crystallinity of the element isolation region is lowered by addition ofthe impurity element; therefore, it can be said that the elementisolation region is made to be amorphous. On the other hand, because theelement region is a crystalline semiconductor layer, in a case where asemiconductor element is Mimed in the element region, crystallinity ofthe channel formation region is higher than that of the elementisolation region, and high electron field-effect mobility can beobtained as a semiconductor element.

As the impurity element added to the element isolation region, a raregas element such as argon (Ar), neon (Ne), krypton (Kr), or xenon (Xe)may be used. By further addition of such a rare gas element that is anelement having comparatively high mass as well as oxygen, nitrogen, andcarbon, a physical impact on the semiconductor layer can be increased,whereby crystallinity of the element isolation region can be loweredmore effectively.

Therefore, with the use of the present invention, a semiconductor layercan be isolated into a plurality of element regions without beingdivided into island shapes, and steps resulting from the edge portion ofthe semiconductor layer are not generated. Thus, an insulating layer canbe formed over a flat semiconductor layer, and the coverage of thesemiconductor layer with the insulating layer can be improved.Therefore, a semiconductor device that is a highly reliablesemiconductor storage device in which defects such as a short andleakage current between a charge accumulation layer, a control gateelectrode layer, a gate electrode layer, and a semiconductor layer thatare caused by a coverage defect of the semiconductor layer with aninsulating layer are prevented and a manufacturing method of such asemiconductor device can be provided. Accordingly, furtherminiaturization and higher integration of the semiconductor devicehaving memory elements are possible, and higher performance of thesemiconductor device can be achieved. In addition, because defects suchas shape defects of the film can be reduced, in the manufacturingprocess, the semiconductor device can be manufactured with good yield.

This embodiment mode can be combined with other embodiment modesdisclosed in this specification.

Embodiment Mode 10

In this embodiment mode, as a semiconductor device in which defects suchas a short and leakage current between a charge accumulation layer, acontrol gate electrode layer, and a semiconductor layer that are causedby a coverage defect of a semiconductor layer with an insulating layerare prevented, an example of other nonvolatile semiconductor storagedevices will be described with reference to drawings.

The memory elements shown in Embodiment Modes 2 to 9 each show anexample in which metal or a semiconductor material is used as a chargeaccumulation layer. In this embodiment mode, an insulating layer, forexample, an insulating layer including a conductive particle or asemiconductor particle such as silicon or germanium is used as a chargeaccumulation layer.

The charge accumulation layer is applied to a nonvolatile semiconductorstorage device according to the present invention for chargeaccumulation. However, other materials can be applied as long as theyhave a similar function. The charge accumulation layer can be formedusing an insulating layer having a defect that traps charges in a filmor an insulating layer including a conductive particle or asemiconductor particle such as silicon or germanium. Representativeexamples of such materials are a silicon compound and a germaniumcompound. As a silicon compound, there are silicon nitride to whichoxygen is added, silicon oxide to which nitrogen is added, siliconnitride to which oxygen and hydrogen are added, silicon oxide to whichnitrogen and hydrogen are added, and the like. As a germanium compound,there are germanium nitride, germanium oxide, germanium nitride to whichoxygen is added, germanium oxide to which nitrogen is added, germaniumnitride to which oxygen and hydrogen are added, germanium oxide to whichnitrogen and hydrogen are added, and the like. Further, a germaniumparticle or a silicon germanium particle may be included in the chargeaccumulation layer.

Also in the memory element in this embodiment mode, an element isolationregion including first and second impurity elements is formed in thesemiconductor layer, and element regions that are insulated and isolatedare used.

The element isolation region is formed by selective addition of a firstimpurity element that does not contribute to conductivity and a secondimpurity element that imparts an opposite conductivity type to that of asource region and a drain region in the element region in order toelectrically isolate elements from each other in one semiconductorlayer.

As the first impurity element that does not contribute to conductivity,an impurity element of at least one or more kinds of oxygen, nitrogen,and carbon can be used. The element isolation region to which the firstimpurity element is added, conductivity is lowered by mixture of thefirst impurity element that does not contribute to conductivity, andresistance of the element isolation region is increased because itscrystallinity is lowered by a physical impact (it can also be referredto as a so-called sputtering effect) on the semiconductor layer atadding. In the element isolation region with the increased resistance,electron field-effect mobility is also lowered, and accordingly,elements can be electrically isolated from each other. On the otherhand, in a region to which an impurity element is not added, electronfield-effect mobility that is high enough to be able to serve as anelement is kept, and accordingly, the region can be used as an elementregion.

The element region has a source region, a drain region, and a channelformation region. The source region and the drain region are impurityregions having one conductivity type (for example, n-type impurityregions or p-type impurity regions).

An impurity element that imparts an opposite conductivity type to thatof the source region and the drain region in the element region is addedto the element isolation region, whereby the element isolation region ismade to be an impurity region having an opposite conductivity type tothat of the source region and the drain region in the element regionthat is adjacent to the element isolation region. That is, in a casewhere the source region and the drain region in the element region aren-type impurity regions, the adjacent element isolation region may beformed as a p-type impurity region. Similarly, in a case where thesource region and the drain region in the element region are p-typeimpurity regions, the adjacent element isolation region may be formed asan n-type impurity region. The element region and the element isolationregion that are adjacent to each other form a PN junction. Accordingly,the element regions can be further insulated and isolated from eachother by the element isolation region provided between the elementregions.

One feature of the present invention is that one semiconductor layer isisolated into a plurality of element regions in the manner thatresistance of the element isolation region by which the element regionsare insulated and isolated from each other is increased by addition ofthe first impurity element that does not contribute to conductivity, andfurther, PN junctions are successively (repeadedly) formed in positionswhere the element region and the element isolation region are in contactwith each other by addition of the second impurity element that impartsan opposite conductivity type to that of the source region and the drainregion in the element region. By the present invention, the elementregions can be isolated from each other by an effect caused by each ofthe first impurity element and the second impurity element. Thus, ahigher effect of insulation and isolation of the element can beobtained.

The resistivity of the element isolation region is preferably greaterthan or equal to 1×10¹⁰ Ω·cm, and the concentration of the impurityelement such as oxygen, nitrogen, or carbon is preferably greater thanor equal to 1×10²⁰ Ω·cm⁻³ and less than 4×10²² Ω·cm⁻³.

Crystallinity of the element isolation region is lowered by addition ofthe impurity element; therefore, it can be said that the elementisolation region is made to be amorphous. On the other hand, because theelement region is a crystalline semiconductor layer, in a case where asemiconductor element is formed in the element region, crystallinity ofthe channel formation region is higher than that of the elementisolation region, and high electron field-effect mobility can beobtained as a semiconductor element.

As the impurity element added to the element isolation region, a raregas element such as argon (Ar), neon (Ne), krypton (Kr), or xenon (Xe)may be used. By further addition of such a rare gas element that is anelement having comparatively high mass as well as oxygen, nitrogen, andcarbon, a physical impact on the semiconductor layer can be increased,whereby crystallinity of the element isolation region can be loweredmore effectively.

Therefore, with the use of the present invention, a semiconductor layercan be isolated into a plurality of element regions without beingdivided into island shapes, and steps resulting from the edge portion ofthe semiconductor layer are not generated. Thus, an insulating layer canbe formed over a flat semiconductor layer, and the coverage of thesemiconductor layer with the insulating layer can be improved.Therefore, a semiconductor device that is a highly reliablesemiconductor storage device in which defects such as a short andleakage current between a gate electrode layer and a semiconductor layerthat are caused by a coverage defect of the semiconductor layer with aninsulating layer are prevented and a manufacturing method of such asemiconductor device can be provided. Accordingly, furtherminiaturization and higher integration of the semiconductor devicehaving memory elements are possible, and higher performance of thesemiconductor device can be achieved. In addition, because defects suchas shape defects of the film can be reduced, in the manufacturingprocess, the semiconductor device can be manufactured with good yield.

This embodiment mode can be implemented by being combined with otherembodiment modes disclosed in this specification.

Embodiment Mode 11

In this embodiment mode, an example of a highly reliable semiconductordevice in which defects such as a short and leakage current between agate electrode layer and a semiconductor layer that are caused by acoverage defect of a semiconductor layer with an insulating layer in asemiconductor element are prevented, will be described with reference todrawings.

Embodiment Modes 1 to 10 show an example where a semiconductor layer isprovided over a substrate having an insulating surface. However, thisembodiment mode shows an example of using a semiconductor substrateformed of Si or the like or an SOI substrate instead of theabove-described thin film processes.

An SOI (Silicon on Insulator) substrate in which a single crystallinesemiconductor layer is formed over an insulating surface can be formedusing a method performed by sticking of a wafer or a method called SIMOXin which an insulating layer is formed inside by implantation of anoxygen ion into a Si substrate.

Also in the memory element in this embodiment mode, an element isolationregion including first and second impurity elements is formed in thesemiconductor layer, and element regions in which element isolation isperformed are used.

The element isolation region is formed by selective addition of a firstimpurity element that does not contribute to conductivity and a secondimpurity element that imparts an opposite conductivity type to that of asource region and a drain region in the element region in order toelectrically isolate elements from each other in one semiconductorlayer.

As the first impurity element that does not contribute to conductivity,an impurity element of at least one or more kinds of oxygen, nitrogen,and carbon can be used. The element isolation region to which the firstimpurity element is added, conductivity is lowered by mixture of thefirst impurity element that does not contribute to conductivity, andresistance of the element isolation region is increased because itscrystallinity is lowered by a physical impact (it can also be referredto as a so-called sputtering effect) on the semiconductor layer atadding. In the element isolation region with the increased resistance,electron field-effect mobility is also lowered, and accordingly,elements can be electrically isolated from each other. On the otherhand, in a region to which an impurity element is not added, electronfield-effect mobility that is high enough to be able to serve as anelement is kept, and accordingly, the region can be used as an elementregion.

The element region has a source region, a drain region, and a channelformation region. The source region and the drain region are impurityregions having one conductivity type (for example, n-type impurityregions or p-type impurity regions). An impurity element that imparts anopposite conductivity type to that of the source region and the drainregion in the element region is added to the element isolation region,whereby the element isolation region is made to be an impurity regionhaving an opposite conductivity type to that of the source region andthe drain region in the element region that is adjacent to the elementisolation region. That is, in a case where the source region and thedrain region in the element region are n-type impurity regions, theadjacent element isolation region may be formed as a p-type impurityregion. Similarly, in a case where the source region and the drainregion in the element region are p-type impurity regions, the adjacentelement isolation region may be formed as an n-type impurity region. Theelement region and the element isolation region that are adjacent toeach other form a PN junction. Accordingly, the element regions can befurther insulated and isolated from each other by the element isolationregion provided between the element regions.

One feature of the present invention is that one semiconductor layer isisolated into a plurality of element regions in the manner thatresistance of the element isolation region by which the element regionsare insulated and isolated from each other is increased by addition ofthe first impurity element that does not contribute to conductivity, andfurther, PN junctions are successively (repeadedly) formed in positionswhere the element region and the element isolation region are in contactwith each other by addition of the second impurity element that impartsan opposite conductivity type to that of the source region and the drainregion in the element region. By the present invention, the elementregions can be isolated from each other by an effect caused by each ofthe first impurity element and the second impurity element. Thus, ahigher effect of insulation and isolation of the element can beobtained.

The resistivity of the element isolation region is preferably greaterthan or equal to 1×10¹⁰ Ω·cm, and the concentration of the impurityelement such as oxygen, nitrogen, or carbon is preferably greater thanor equal to 1×10²⁰ Ω·cm⁻³ and less than 4×10²² Ω·cm⁻³.

Crystallinity of the element isolation region is lowered by addition ofthe impurity element; therefore, it can be said that the elementisolation region is made to be amorphous. On the other hand, because theelement region is a crystalline semiconductor layer, in a case where asemiconductor element is formed in the element region, crystallinity ofthe channel formation region is higher than that of the elementisolation region, and high electron field-effect mobility can beobtained as a semiconductor element.

As the impurity element added to the element isolation region, a raregas element such as argon (Ar), neon (Ne), krypton (Kr), or xenon (Xe)may be used. By further addition of such a rare gas element that is anelement having comparatively high mass as well as oxygen, nitrogen, andcarbon, a physical impact on the semiconductor layer can be increased,whereby crystallinity of the element isolation region can be loweredmore effectively.

Therefore, with the use of the present invention, a semiconductor layercan be isolated into a plurality of element regions without beingdivided into island shapes. Further, volume expansion of the elementisolation region does not occur because thermal treatment at hightemperature is not performed, whereby flatness of the surface of thesemiconductor layer (or a semiconductor substrate) is well maintained.Steps resulting from the edge portion of the semiconductor layer are notgenerated. Thus, an insulating layer is formed over a flat semiconductorlayer, leading to improvement in coverage of the semiconductor layerwith the insulating layer. Therefore, a semiconductor device that is ahighly reliable nonvolatile semiconductor storage device in whichdefects such as a short and leakage current between a chargeaccumulation layer, a control gate electrode layer, a gate electrodelayer, and a semiconductor layer that are caused by a coverage defect ofthe semiconductor layer with an insulating layer are prevented and amanufacturing method of such a semiconductor device can be providedwithout conducting a complicated manufacturing process. Accordingly,further miniaturization and higher integration of the semiconductordevice are possible, and higher performance of the semiconductor devicecan be achieved. In addition, since such defects caused by shape defectsof the film can be reduced, in the manufacturing process, thesemiconductor device can be manufactured with good yield.

This embodiment mode can be implemented by being combined with otherembodiment modes disclosed in this specification.

Embodiment Mode 12

In this embodiment mode, examples of the application example of asemiconductor device capable of wireless data communication, whichincludes the above-described nonvolatile semiconductor storage deviceformed using the present invention and the like, will be described. Asemiconductor device capable of wireless data communication is alsocalled an RFID tag, an ID tag, an IC tag, an IC chip, an RF tag, awireless tag, an electronic tag, or a wireless chip depending on the useapplication.

A semiconductor device 800 has a function of wireless datacommunication, and includes a high-frequency circuit 810, a power supplycircuit 820, a reset circuit 830, a clock generation circuit 840, a datademodulation circuit 850, a data modulation circuit 860, a controlcircuit 870 for controlling other circuits, a memory circuit 880, and anantenna 890 (FIG. 22A). The high-frequency circuit 810 is a circuitwhich receives signals from the antenna 890, and outputs signals whichare received from the data modulation circuit 860 to the antenna 890;the power supply circuit 820 is a circuit which generates power supplypotentials from the signals received; the reset circuit 830 is a circuitwhich generates reset signals; the clock generation circuit 840 is acircuit which generates various clock signals based on the signals inputfrom the antenna 890; the data demodulation circuit 850 is a circuitwhich demodulates the signals received and outputs them to the controlcircuit 870; and the data modulation circuit 860 is a circuit whichmodulates the signals received from the control circuit 870. The controlcircuit 870 includes, for example, a code extraction circuit 910, a codejudging circuit 920, a CRC judging circuit 930, and an output unitcircuit 940. It is to be noted that the code extraction circuit 910 is acircuit which extracts a plurality of codes included in the instructionstransmitted to the control circuit 870; the code judging circuit 920 isa circuit which judges the content of the instructions by comparing theextracted code with a reference code; and the CRC judging circuit 930 isa circuit which detects the presence of transmission errors or the likebased on the judged code.

Next, an example of the operation of the above-described semiconductordevice is described. First, the antenna 890 receives a radio signal.When the radio signal is transmitted to the power supply circuit 820through the high-frequency circuit 810, the power supply circuit 820generates a high power supply potential (hereinafter referred to asVDD). VDD is supplied to each circuit included in the semiconductordevice 800. In addition, a signal transmitted to the data demodulationcircuit 850 through the high-frequency circuit 810 is demodulated(hereinafter the signal is referred to as a demodulated signal).Further, a signal transmitted to the reset circuit 830 through thehigh-frequency circuit 810 and the demodulated signal which has passedthrough the clock generation circuit 840 are transmitted to the controlcircuit 870. The signals transmitted to the control circuit 870 areanalyzed by the code extraction circuit 910, the code judging circuit920, the CRC judging circuit 930, and the like. Then, data on thesemiconductor device which is stored in the memory circuit 880 is outputin response to the analyzed signal. The output data of the semiconductordevice is encoded in the output unit circuit 940. Further, the encodeddata of the semiconductor device 800 is modulated in the data modulationcircuit 860, and then transmitted as a radio signal through the antenna890. Note that the low power supply potential (hereinafter referred toas VSS) is common to the plurality of circuits included in thesemiconductor device 800; therefore, GND can be used as the VSS. Inaddition, the nonvolatile semiconductor memory device and the likeformed using the invention can be applied to the memory circuit 880.

In this manner, by communicating signals between the semiconductordevice 800 and a reader/writer, data on the semiconductor device can beread out.

The semiconductor device 800 may be either of a type where power supplyto each circuit is conducted by using electromagnetic waves withoutproviding a built-in battery, or of a built-in battery type where powersupply to each circuit is conducted by using both electromagnetic wavesand a built-in battery.

Next, examples of the application of the semiconductor device which canperform wireless data communication are described. A side surface of aportable terminal which includes a display portion 3210 is provided witha reader/writer 3200, and a side surface of a product 3220 is providedwith a semiconductor device 3230 (FIG. 22B). When the reader/writer 3200is put close to the semiconductor device 3230 provided on the product3220, data on the raw material or source of the product, inspectionresult in each production step, history of the distribution process,product description, and the like is displayed on the display portion3210. In addition, when carrying a product 3260 on a belt conveyor,inspection of the product 3260 can be conducted by using a reader/writer3240 and a semiconductor device 3250 provided on the product 3260 (FIG.22C). In this manner, by using the semiconductor device for a system,data acquisition can be easily conducted, and thus a higher function andhigher added value can be realized.

A nonvolatile semiconductor storage device or the like which is asemiconductor device formed using the present invention can be appliedto various fields of electronic devices having memories. For example,the nonvolatile semiconductor storage device of the present inventioncan be applied to electronic devices such as cameras (e.g., videocameras or digital cameras), goggle displays (e.g., head mounteddisplays), navigation systems, audio reproducing apparatuses (e.g., caraudio or audio component sets), computers, game machines, portableinformation terminals (e.g., mobile computers, mobile phones, portablegame machines, or electronic books), and image reproducing devicesprovided with storage media (specifically, a device for reproducing thecontent of a storage medium such as a DVD (Digital Versatile Disc) andhaving a display for displaying the reproduced image). FIGS. 23A to 23Eshow specific examples of such electronic devices.

FIGS. 23A and 23B show digital cameras. FIG. 23B shows a rear side ofFIG. 23A. This digital camera includes a housing 2111, a display portion2112, a lens 2113, operating keys 2114, a shutter 2115, and the like. Inaddition, the digital camera also includes a removable nonvolatilememory 2116, and data picked up by the digital camera is stored in thememory 2116. A nonvolatile semiconductor storage device or the likewhich is a semiconductor device formed using the present invention canbe applied to the memory 1225.

FIG. 23C shows a mobile phone which is one typical example of a portableterminal. This mobile phone includes a housing 2121, a display portion2122, operating keys 2123, and the like. In addition, the mobile phonealso includes a removable nonvolatile memory 2125, and data such as thephone number of the mobile phone, image data, audio data, and the likecan be stored in the memory 2125 and reproduced. A nonvolatilesemiconductor storage device or the like which is a semiconductor deviceformed using the present invention can be applied to the memory 2125.

FIG. 23D shows a digital player which is one typical example of an audiodevice. The digital player shown in FIG. 23D includes a main body 2130,a display portion 2131, a memory portion 2132, operating portions 2133,a pair of earphones 2134, and the like. It is to be noted that insteadof the pair of earphones 2134, headphones or wireless earphones can beused. A nonvolatile semiconductor storage device or the like that is asemiconductor device formed using the present invention can be appliedto the memory portion 2132. In addition, by using a NAND-typenonvolatile memory with a storage capacity of 20 to 200 gigabytes (GB),and operating the operating portions 2133, images or audio (music) canbe recorded and reproduced. It is to be noted that by displaying whitetext on a black background of the display portion 2131, powerconsumption can be suppressed. This is particularly effective for theportable audio device. Note also that the nonvolatile semiconductorstorage device provided in the memory portion 2132 may be removable.

FIG. 23E shows an e-book device (also called an e-book reader). Thise-book device includes a main body 2141, a display portion 2142,operating keys 2143, and a memory portion 2144. In addition, a modem maybe built into the main body 2141, or a structure capable of wirelessdata transmission/reception may be employed. A nonvolatile semiconductorstorage device or the like which is a semiconductor device formed usingthe present invention can be applied to the memory portion 2144. Inaddition, by using a NAND-type nonvolatile memory with a storagecapacity of 20 to 200 gigabytes (GB), and operating the operating keys2143, images or audio (music) can be recorded and reproduced. It is tobe noted that the nonvolatile semiconductor storage device provided inthe memory portion 2144 may be removable.

As described above, the applicable range of the semiconductor device ofthe present invention (in particular, a nonvolatile semiconductorstorage device or the like which is a semiconductor device formed usingthe present invention) is so wide that the semiconductor device can beapplied to various fields of electronic devices having memories.

Embodiment Mode 13

According to the present invention, a semiconductor device serving as achip including a processor circuit (hereinafter also called a processorchip, a wireless chip, a wireless processor, a wireless memory, or awireless tag) can be formed. The semiconductor device of the presentinvention can be used for various applications. For example, the presentinvention can be applied to bills, coins, securities, documents, bearerbonds, packaging containers, books, storage media, personal belongings,vehicles, foods, clothes, healthcare items, consumer products, medicals,electronic devices, and the like.

A semiconductor device having memory elements faulted using the presentinvention can be freely transferred to various substrates. Therefore,inexpensive materials can be selected for the substrate, and thesemiconductor device can be provided with various functions according tothe intended use, and further, the semiconductor device can bemanufactured at low cost. Therefore, since a chip including a processorcircuit according to the present invention has characteristics of a lowcost, compact size, thin body, and lightweight, it is suitable forbills, coins, books which are often carried about, personal belongings,clothes, and the like.

The bills and coins are currency in the market and include notes thatare circulating as the real money in specific areas (cash vouchers),memorial coins, and the like. The securities include checks,certificates, promissory notes, and the like, and can be provided with achip 190 including a processor circuit (FIG. 21A). The documents includedriver's licenses, resident's cards, and the like, and can be providedwith a chip 191 including a processor circuit (see FIG. 21B). Thepersonal belongings include shoes, a pair of glasses, and the like, andcan be provided with a chip 197 including a processor circuit (see FIG.21C). The bearer bonds include stamps, rice coupons, various giftcoupons, and the like. The packaging containers include paper forwrapping a lunch box or the like, plastic bottles, and the like, and canbe provided with a chip 193 including a processor circuit (see FIG.21D). The books include documents and the like, and can be provided witha chip 194 including a processor circuit (see FIG. 21E). The storagemedia include DVD software, video tapes, and the like, and can beprovided with a chip 195 including a processor circuit (see FIG. 21F).The means of transportation include wheeled cycles or vehicles such asbicycles, vessels, and the like, and can be provided with a chip 196including a processor circuit (see FIG. 21G). The foods include fooditems, beverages, and the like. The clothes include clothing, footwear,and the like. The healthcare items include medical devices, healthappliances, and the like. The consumer products include furniture,lighting apparatuses, and the like. The medicals include medicines,agricultural chemicals, and the like. The electronic devices includeliquid crystal display devices, EL display devices, television sets(television receivers or thin television receivers), mobile phones, andthe like.

The semiconductor device of the present invention is mounted on aprinted board, attached to a surface of a product, or embedded in aproduct, so that it is fixed on the product. For example, thesemiconductor device of the present invention is embedded in paper of abook or an organic resin of a package. The semiconductor device of thepresent invention can realize a compact size, slim body, andlightweight. Therefore, even when it is fixed on a product, the designof the product itself will not be spoiled. In addition, when thesemiconductor device of the present invention is applied to bills,coins, securities, bearer bonds, documents, and the like, authenticationfunctions can be provided. In addition, when the semiconductor device ofthe present invention is applied to packaging containers, storage media,personal belongings, foods, clothes, consumer products, electronicdevices, and the like, efficiency of a system such as an inspectionsystem can be increased.

This application is based on Japanese Patent Application serial No.2006-126984 filed in Japan Patent Office on Apr. 28, 2006, the entirecontents of which are hereby incorporated by reference.

1. A manufacturing method of a semiconductor device comprising the stepsof: forming a semiconductor layer over an insulating surface, forming anelement region and an element isolation region including a firstimpurity element and a second impurity element in the semiconductorlayer by selective addition of the first impurity element of at leastone or more kinds of oxygen, nitrogen, and carbon and the secondimpurity element that imparts one conductivity type, to thesemiconductor layer, forming an insulating layer over the element regionand the element isolation region, forming a conductive layer over theelement region and the insulating layer, and forming a source region anda drain region having an opposite conductivity type to that of thesecond impurity element in the element region.
 2. The manufacturingmethod of a semiconductor device according to claim 1, wherein theinsulating layer is formed by plasma treatment under a nitrogenatmosphere or an oxygen atmosphere.
 3. The manufacturing method of asemiconductor device according to claim 1, wherein concentration of thefirst impurity element included in the element isolation region isgreater than or equal to 1×10²⁰ Ω·cm⁻³ and less than 4×10²² Ω·cm⁻³. 4.The manufacturing method of a semiconductor device according to claim 1,wherein the source region and the drain region are formed by addition ofan impurity element that imparts an opposite conductivity type to thatof the second impurity element to the element region.
 5. A manufacturingmethod of a semiconductor device comprising the steps of: forming asemiconductor layer over an insulating surface, forming an insulatinglayer over the semiconductor layer, forming an element region and anelement isolation region including a first impurity element and a secondimpurity element in the semiconductor layer by selective addition of thefirst impurity element of at least one or more kinds of oxygen,nitrogen, and carbon and the second impurity element that imparts oneconductivity type, to the semiconductor layer through the insulatinglayer, forming a conductive layer over the element region and theinsulating layer, and forming a source region and a drain region havingan opposite conductivity type to that of the second impurity element inthe element region.
 6. The manufacturing method of a semiconductordevice according to claim 5, wherein the insulating layer is formed byplasma treatment under a nitrogen atmosphere or an oxygen atmosphere. 7.The manufacturing method of a semiconductor device according to claim 5,wherein concentration of the first impurity element included in theelement isolation region is greater than or equal to 1×10²⁰ Ω·cm⁻³ andless than 4×10²² Ω·cm⁻³.
 8. The manufacturing method of a semiconductordevice according to claim 5, wherein the source region and the drainregion are formed by selective addition of an impurity element thatimparts an opposite conductivity type to that of the second impurityelement to the element region.
 9. A manufacturing method of asemiconductor device comprising the steps of: selectively adding a firstimpurity element of at least one or more kinds of oxygen, nitrogen, andcarbon and a second impurity element that imparts one conductivity type,to a semiconductor to form an element isolation region; and forming anelement region in the semiconductor wherein the element region includesa channel region, a source region and a drain region, wherein the sourceregion and the drain region have an opposite conductivity type to theconductivity type of the second impurity element, and wherein theelement isolation region is in contact with one of the source region andthe drain region.